// Om Namah Shivaya
// GM in 127 days
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define endl '\n'
#define pb push_back
#define conts continue
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "YES" << endl
#define no cout << "NO" << endl
#define ff first
#define ss second
#define ceil2(x,y) ((x+y-1) / (y))
#define sz(a) a.size()
#define setbits(x) __builtin_popcountll(x)
#ifndef ONLINE_JUDGE
#define debug(x) cout << #x <<" = "; print(x); cout << endl
#else
#define debug(x)
#endif
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
bool iseven(ll n) {if ((n & 1) == 0) return true; return false;}
void print(ll t) {cout << t;}
void print(int t) {cout << t;}
void print(string t) {cout << t;}
void print(char t) {cout << t;}
void print(double t) {cout << t;}
void print(ld t) {cout << t;}
template <class T, class V> void print(pair <T, V> p);
template <class T> void print(vector <T> v);
template <class T> void print(set <T> v);
template <class T, class V> void print(map <T, V> v);
template <class T> void print(multiset <T> v);
template <class T, class V> void print(pair <T, V> p) {cout << "{"; print(p.ff); cout << ","; print(p.ss); cout << "}";}
template <class T> void print(vector <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T> void print(set <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T> void print(multiset <T> v) {cout << "[ "; for (T i : v) {print(i); cout << " ";} cout << "]";}
template <class T, class V> void print(map <T, V> v) {cout << "[ "; for (auto i : v) {print(i); cout << " ";} cout << "]";}
template<typename T> void amin(T &a, T b) { a = min(a, b); }
template<typename T> void amax(T &a, T b) { a = max(a, b); }
void usaco(string filename) {
freopen((filename + ".in").c_str(), "r", stdin);
freopen((filename + ".out").c_str(), "w", stdout);
}
const int MOD = 1e9 + 7;
const int maxn = 1e5 + 5;
const int inf1 = 1e9 + 5;
const ll inf2 = ll(1e18) + 5;
template<typename T>
struct lazysegtree {
/*=======================================================*/
struct data {
ll a;
};
struct lazy {
ll a;
};
data d_neutral = {0};
lazy l_neutral = {0};
void merge(data &curr, data &left, data &right) {
curr.a = left.a + right.a;
}
void create(int x, int lx, int rx, T v) {
tr[x].a = v;
}
void modify(int x, int lx, int rx, T v) {
lz[x].a += v;
}
void propagate(int x, int lx, int rx) {
ll val = lz[x].a;
if (val == 0) return;
tr[x].a += val;
if (rx - lx > 1) {
lz[2 * x + 1].a += val;
lz[2 * x + 2].a += val;
}
lz[x] = l_neutral;
}
/*=======================================================*/
int siz = 1;
vector<data> tr;
vector<lazy> lz;
lazysegtree(int n) {
while (siz < n) siz *= 2;
tr.assign(2 * siz, d_neutral);
lz.assign(2 * siz, l_neutral);
}
void build(vector<T> &a, int n, int x, int lx, int rx) {
if (rx - lx == 1) {
if (lx < n) {
create(x, lx, rx, a[lx]);
}
return;
}
int mid = (lx + rx) / 2;
build(a, n, 2 * x + 1, lx, mid);
build(a, n, 2 * x + 2, mid, rx);
merge(tr[x], tr[2 * x + 1], tr[2 * x + 2]);
}
void build(vector<T> &a, int n) {
build(a, n, 0, 0, siz);
}
void rupd(int l, int r, T v, int x, int lx, int rx) {
propagate(x, lx, rx);
if (lx >= r or rx <= l) return;
if (lx >= l and rx <= r) {
modify(x, lx, rx, v);
propagate(x, lx, rx);
return;
}
int mid = (lx + rx) / 2;
rupd(l, r, v, 2 * x + 1, lx, mid);
rupd(l, r, v, 2 * x + 2, mid, rx);
merge(tr[x], tr[2 * x + 1], tr[2 * x + 2]);
}
void rupd(int l, int r, T v) {
rupd(l, r + 1, v, 0, 0, siz);
}
data query(int l, int r, int x, int lx, int rx) {
propagate(x, lx, rx);
if (lx >= r or rx <= l) return d_neutral;
if (lx >= l and rx <= r) return tr[x];
int mid = (lx + rx) / 2;
data curr;
data left = query(l, r, 2 * x + 1, lx, mid);
data right = query(l, r, 2 * x + 2, mid, rx);
merge(curr, left, right);
return curr;
}
data query(int l, int r) {
return query(l, r + 1, 0, 0, siz);
}
};
void solve(int test_case)
{
ll n; cin >> n;
vector<ll> a(n + 5);
rep1(i, n) cin >> a[i];
lazysegtree<ll> st(n + 5);
st.build(a, n + 5);
vector<ll> prefops(n + 5), prefend(n + 5), prefadd(n + 5);
rep1(i, n) {
ll prev = st.query(i - 1, i - 1).a;
ll curr = st.query(i, i).a;
if (curr > prev) {
prefend[i] = curr;
prefadd[i] = curr - a[i];
conts;
}
ll toadd = prev + 1 - curr;
st.rupd(i, n, toadd);
prefops[i] = toadd;
prefend[i] = curr + toadd;
prefadd[i] = curr + toadd - a[i];
}
vector<ll> suffops(n + 5), suffend(n + 5), suffadd(n + 5);
st = lazysegtree<ll>(n + 5);
st.build(a, n + 5);
rev(i, n, 1) {
ll prev = st.query(i + 1, i + 1).a;
ll curr = st.query(i, i).a;
if (curr > prev) {
suffend[i] = curr;
suffadd[i] = curr - a[i];
conts;
}
ll toadd = prev + 1 - curr;
st.rupd(1, i, toadd);
suffops[i] = toadd;
suffend[i] = curr + toadd;
suffadd[i] = curr + toadd - a[i];
}
rep1(i, n) prefops[i] += prefops[i - 1];
rev(i, n, 1) suffops[i] += suffops[i + 1];
ll ans = inf2;
prefend[0] = inf2;
rep(i, n + 1) {
ll res = prefops[i] + suffops[i + 1];
res += max(suffend[i + 1] + 1 - prefend[i], 0ll);
res -= min(prefops[i], suffops[i + 1]);
amin(ans, res);
}
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
