#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;
const int maxn = 500001;
int dist[maxn];
int seg_ind[maxn];
bool was_del[maxn];
set<int> not_take[maxn];
int take[maxn];
const int tree_siz = 1024*1024-1;
int min_[tree_siz+1];
int oper[tree_siz+1];
void spych(int v)
{
min_[v*2] += oper[v];
min_[v*2+1] += oper[v];
oper[v*2] += oper[v];
oper[v*2+1] += oper[v];
oper[v] = 0;
}
int get_seg(int akt, int p1, int p2, int s1, int s2)
{
if(p2 < s1 || p1 > s2) return 1e9;
if(p1 >= s1 && p2 <= s2)
{
return min_[akt];
}
spych(akt);
return min(get_seg(akt*2,p1,(p1+p2)/2,s1,s2),get_seg(akt*2+1,(p1+p2)/2+1,p2,s1,s2));
}
void change_min(int akt, int p1, int p2, int s1, int s2, int w)
{
if(s1 > s2) return;
if(p2 < s1 || p1 > s2) return;
if(p1 >= s1 && p2 <= s2)
{
oper[akt] += w;
min_[akt] += w;
return;
}
spych(akt);
change_min(akt*2,p1,(p1+p2)/2,s1,s2,w);
change_min(akt*2+1,(p1+p2)/2+1,p2,s1,s2,w);
min_[akt] = min(min_[akt*2],min_[akt*2+1]);
}
int n;
int c_left[maxn];
int c_right[maxn];
void add_left(int v, int k)
{
if(k == 0) return;
c_left[v] += k;
take[v] += k;
change_min(1,0,tree_siz/2,v+1,n,-dist[v]*k*2);
int d = 1;
if(k < 0) d = -1;
change_min(1,0,tree_siz/2,v,v,-dist[v]*2*(k-d));
}
void add_right(int v, int k)
{
if(k == 0) return;
c_right[v] += k;
take[v] += k;
change_min(1,0,tree_siz/2,v+1,n,-dist[v]*k*2);
change_min(1,0,tree_siz/2,v,v,-dist[v]*(2*k));
}
bool valid()
{
return get_seg(1,0,tree_siz/2,0,n-1) >= 0;
}
int main()
{
//ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//random_start();
cin >> n;
ll sum = 0;
ll ans = 0;
vl arr(n);
rep(i,n) cin >> arr[i];
rep(i,n) if(arr[i] != -1) sum += arr[i];
int pop = -1e7;
rep(i,n) dist[i] = 1e7;
rep(i,n)
{
if(arr[i] == -1) pop = i;
else dist[i] = min(dist[i],i-pop);
}
pop = 1e7;
for(int i = n-1; i >= 0; i--)
{
if(arr[i] == -1) pop = i;
else
{
dist[i] = min(dist[i],pop-i);
}
}
rep(i,n+1) change_min(1,0,tree_siz/2,i,i,1e7+i);
vector<pii> segs;
int start = 0;
rep(i,n)
{
if(arr[i] == -1)
{
if(start != i)
{
segs.pb({start,i-1});
}
start = i+1;
}
}
if(start != n) segs.pb({start,n-1});
rep(i,siz(segs))
{
rep2(j,segs[i].ff,segs[i].ss)
{
if(arr[j] != 0) not_take[i].insert(j);
seg_ind[j] = i;
}
if(siz(not_take[i]) != 0 && segs[i].ss != n-1)
{
int nt = *(--not_take[i].end());
change_min(1,0,tree_siz/2,nt,nt,-1e7);
ans++;
}
}
vector<pii> v_sort;
rep(i,n)
{
if(arr[i] > 0)
{
v_sort.pb({dist[i],i});
}
}
sort(all(v_sort));
forall(it,v_sort)
{
int v = it.ss;
int s = seg_ind[v];
int mid = (segs[s].ff+segs[s].ss+1)/2;
if(segs[s].ss == n-1) mid = n;
if(segs[s].ff == 0) mid = -1;
int k = 0;
if(v < mid)
{
//left
rep2(i,1,arr[v])
{
add_left(v,i);
bool is = 1;
int nt = *(--not_take[s].end());
if(mid != n)
{
if(nt == v)
{
if(i == arr[v])
{
not_take[s].erase(v);
is = 0;
}
else
{
change_min(1,0,tree_siz/2,v,v,-dist[v]*2);
}
}
else
{
if(arr[v] == i) not_take[s].erase(v);
change_min(1,0,tree_siz/2,v,v,-1e7);
}
}
else
{
change_min(1,0,tree_siz/2,v,v,-1e7);
}
is = is && valid();
add_left(v,-i);
if(mid != n)
{
if(nt == v)
{
if(i == arr[v])
{
is = 0;
not_take[s].insert(v);
}
else
{
change_min(1,0,tree_siz/2,v,v,dist[v]*2);
}
}
else
{
if(arr[v] == i) not_take[s].insert(v);
change_min(1,0,tree_siz/2,v,v,1e7);
}
}
else
{
change_min(1,0,tree_siz/2,v,v,1e7);
}
if(!is) break;
k++;
ans++;
}
if(k != 0)
{
add_left(v,k);
int nt = *(--not_take[s].end());
if(mid != n)
{
if(nt == v)
{
change_min(1,0,tree_siz/2,v,v,-dist[v]*2);
}
else
{
if(k == arr[v]) not_take[s].erase(v);
change_min(1,0,tree_siz/2,v,v,-1e7);
}
}
else
{
change_min(1,0,tree_siz/2,v,v,-1e7);
}
}
}
else
{
//right
rep2(i,1,arr[v])
{
add_right(v,i);
bool is = 1;
int nt = *(--not_take[s].end());
if(nt == v)
{
if(i == arr[v])
{
not_take[s].erase(v);
if(siz(not_take[s]) == 0) is = 0;
else
{
int nt2 = *(--not_take[s].end());
if(take[nt2] == 0) change_min(1,0,tree_siz/2,nt2,nt2,-1e7);
if(nt2 < mid && take[nt2] > 0) change_min(1,0,tree_siz/2,nt2,nt2,-dist[nt2]);
}
}
}
else
{
if(i == arr[v]) not_take[s].erase(v);
change_min(1,0,tree_siz/2,v,v,-1e7);
}
is = is && valid();
add_right(v,-i);
if(nt == v)
{
if(i == arr[v])
{
if(siz(not_take[s]) == 0) is = 0;
else
{
int nt2 = *(--not_take[s].end());
if(take[nt2] == 0) change_min(1,0,tree_siz/2,nt2,nt2,1e7);
if(nt2 < mid && take[nt2] > 0) change_min(1,0,tree_siz/2,nt2,nt2,dist[nt2]);
}
not_take[s].insert(v);
}
}
else
{
if(i == arr[v]) not_take[s].insert(v);
change_min(1,0,tree_siz/2,v,v,1e7);
}
if(!is) break;
k++;
ans++;
}
if(k != 0)
{
add_right(v,k);
int nt = *(--not_take[s].end());
if(nt == v)
{
if(k == arr[v])
{
not_take[s].erase(v);
int nt2 = *(--not_take[s].end());
if(take[nt2] == 0) change_min(1,0,tree_siz/2,nt2,nt2,-1e7);
if(nt2 < mid && take[nt2] > 0) change_min(1,0,tree_siz/2,nt2,nt2,-dist[nt2]);
}
}
else
{
if(k == arr[v]) not_take[s].erase(v);
change_min(1,0,tree_siz/2,v,v,-1e7);
}
}
}
}
cout << sum-ans;
}
