// Hallelujah, praise the one who set me free
// Hallelujah, death has lost its grip on me
// You have broken every chain, There's salvation in your name
// Jesus Christ, my living hope
#include <bits/stdc++.h>
using namespace std;
#define REP(i, s, e) for (int i = (s); i < (e); i++)
#define RREP(i, s, e) for (int i = (s); i >= (e); i--)
template <class T>
inline bool mnto(T& a, T b) {return a > b ? a = b, 1 : 0;}
template <class T>
inline bool mxto(T& a, T b) {return a < b ? a = b, 1: 0;}
typedef long long ll;
typedef long double ld;
#define FI first
#define SE second
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> iii;
#define ALL(_a) _a.begin(), _a.end()
#define SZ(_a) (int) _a.size()
#define pb push_back
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ii> vii;
typedef vector<iii> viii;
#ifndef DEBUG
#define cerr if (0) cerr
#endif
const int INF = 1000000005;
const ll LINF = 1000000000000000005ll;
const int MAXN = 500005;
int n;
int a[MAXN];
int lft[MAXN], rht[MAXN];
int grp[MAXN], cnt[MAXN];
bool done[MAXN];
int donewalk[MAXN];
ll ans;
int fw[MAXN];
void fincre(int i, int x) {
i++;
for (; i <= n; i += i & -i) {
fw[i] += x;
}
}
void fincre(int s, int e, int x) {
fincre(s, x);
fincre(e + 1, -x);
}
int fqsm(int i) {
i++;
int res = 0;
for (; i > 0; i -= i & -i) {
res += fw[i];
}
return res;
}
#define MLR int mid = lo + hi >> 1, lc = u << 1, rc = u << 1 ^ 1
int st[MAXN * 4], lz[MAXN * 4];
void propo(int u, int lo, int hi) {
if (lz[u] == 0) {
return;
}
MLR;
st[lc] += lz[u];
lz[lc] += lz[u];
st[rc] += lz[u];
lz[rc] += lz[u];
lz[u] = 0;
}
void upd(int p, int x, int u = 1, int lo = 0, int hi = n - 1) {
if (lo == hi) {
st[u] = x;
return;
}
MLR;
propo(u, lo, hi);
if (p <= mid) {
upd(p, x, lc, lo, mid);
} else {
upd(p, x, rc, mid + 1, hi);
}
st[u] = min(st[lc], st[rc]);
}
void incre(int s, int e, int x, int u = 1, int lo = 0, int hi = n - 1) {
if (lo >= s && hi <= e) {
st[u] += x;
lz[u] += x;
return;
}
MLR;
propo(u, lo, hi);
if (s <= mid) {
incre(s, e, x, lc, lo, mid);
}
if (e > mid) {
incre(s, e, x, rc, mid + 1, hi);
}
st[u] = min(st[lc], st[rc]);
}
int qmn(int s, int e, int u = 1, int lo = 0, int hi = n - 1) {
if (lo >= s && hi <= e) {
return st[u];
}
MLR;
propo(u, lo, hi);
int res = INF;
if (s <= mid) {
mnto(res, qmn(s, e, lc, lo, mid));
}
if (e > mid) {
mnto(res, qmn(s, e, rc, mid + 1, hi));
}
return res;
}
int main() {
#ifndef DEBUG
ios::sync_with_stdio(0), cin.tie(0);
#endif
cin >> n;
ll tot = 0;
REP (i, 0, n) {
cin >> a[i];
if (a[i] > 0) {
tot += a[i];
}
}
int prv = -INF;
int gc = 0;
REP (i, 0, n) {
if (a[i] == -1) {
prv = i;
gc++;
}
lft[i] = prv;
grp[i] = gc;
}
prv = INF;
RREP (i, n - 1, 0) {
if (a[i] == -1) {
prv = i;
}
rht[i] = prv;
}
vi id, pos;
REP (i, 0, n) {
if (a[i] <= 0) {
continue;
}
cnt[grp[i]]++;
id.pb(i);
pos.pb(i);
}
sort(ALL(id), [&] (int l, int r) {
return ii{min(l - lft[l], rht[l] - l), -l} <
ii{min(r - lft[r], rht[r] - r), -r};
});
REP (i, 1, n) {
fincre(i, n - 1, 1);
}
REP (i, 0, n) {
upd(i, INF);
}
for (int i : id) {
cerr << i << '\n';
done[i] = 1;
int w = 2 * min(i - lft[i], rht[i] - i);
// x <= a[i]
int mn = qmn(i + 1, n - 1);
assert(mn >= 0);
// x * w <= mn
// x <= floor(mn / w)
int x1 = mn / w;
int ct = fqsm(i);
if (ct > 2 * i) {
continue;
}
if (i - lft[i] <= rht[i] - i) { // left cycle
if (donewalk[grp[i]] && donewalk[grp[i]] < i) {
continue;
}
auto apply = [&] (int x, bool walk) {
if (x + walk == 0) {
return;
}
if (walk) {
donewalk[grp[i]] = i;
}
cerr << "APPLY: " << x << ' ' << walk << '\n';
ans += x + walk;
fincre(i, n - 1, x * w);
incre(i, n - 1, -x * w);
// ct + (x - 1) * w + upd <= 2 * i
assert(ct + (x - 1 + walk) * w <= 2 * i);
upd(i, 2 * i - (ct + (x - 1 + walk) * w));
};
// ct + (x - 1) * w <= 2 * i
// x <= (2 * i - ct) / w + 1
int x2 = (2 * i - ct) / w + 1;
if (a[i] < min(x1, x2)) {
auto ptr = upper_bound(ALL(pos), i);
bool walk = 0;
if (ptr == pos.end() || grp[*ptr] != grp[i] || done[*ptr]) {
walk = 1;
}
if (donewalk[grp[i]]) {
walk = 0;
}
apply(a[i] - walk, walk);
continue;
}
if (rht[i] == INF) {
apply(min(x1, x2), 0);
continue;
}
if (x1 < x2) { // stopped by suffix but still have extra for walk
auto ptr = upper_bound(ALL(pos), i);
bool walk = 0;
if (ptr == pos.end() || grp[*ptr] != grp[i] || done[*ptr]) {
walk = 1;
}
if (donewalk[grp[i]]) {
walk = 0;
}
if (a[i] == x1 && walk) {
apply(x1 - 1, 1);
} else {
apply(x1, walk);
}
continue;
}
// no extra for walk unless replace one cycle with walk
int nct = ct + x2 * w;
// nct + j - i <= 2 * j
// nct - i <= j
int j = nct - i;
auto ptr = lower_bound(ALL(pos), j);
bool walk = 0;
if (ptr == pos.end() || grp[*ptr] != grp[i] || done[*ptr]) {
walk = 1;
}
if (donewalk[grp[i]]) {
walk = 0;
}
apply(x2 - walk, walk);
} else { // right cycle
if (donewalk[grp[i]] && donewalk[grp[i]] > i) {
continue;
}
auto apply = [&] (int x) {
if (x == 0) {
return;
}
cerr << "APPLY: " << x << '\n';
ans += x;
fincre(i, n - 1, x * w);
incre(i, n - 1, -x * w);
// ct + x * w + upd <= 2 * i
assert(ct + x * w <= 2 * i);
upd(i, 2 * i - (ct + x * w));
};
auto ptr = lower_bound(ALL(pos), i);
bool walk = 0;
if (ptr == pos.begin() || grp[*prev(ptr)] != grp[i] ||
done[*prev(ptr)] || fqsm(*prev(ptr)) > 2 * (*prev(ptr))) {
walk = 1;
}
if (donewalk[grp[i]]) {
walk = 0;
}
if (walk) {
cerr << "WALK\n";
donewalk[grp[i]] = i;
a[i]--;
ans++;
// ct + upd <= 2 * i
upd(i, 2 * i - ct);
}
// ct + x * w <= 2 * i
// x <= (2 * i - ct) / w
int x2 = (2 * i - ct) / w;
apply(min({a[i], x1, x2}));
}
}
cout << tot - ans << '\n';
return 0;
}
