#include <bits/stdc++.h> using namespace std; const long long MAX = 2e5 + 5; long long vt[MAX], vs[MAX], sv[MAX], vtt[MAX]; void solve() { long long n; cin >> n; for (long long i = 1; i <= n; i++) cin >> vt[i]; for (long long i = 1; i < n; i++) vs[i] = vt[i + 1] - vt[i]; for (long long i = 1; i < n; i++) { if (vs[i] <= 0) { sv[i + 1] = 1 - vs[i] + sv[i]; } else sv[i + 1] = sv[i]; } for (long long i = n - 1; i > 0; i--) { if (vs[i] >= 0) { vtt[i] = vtt[i + 1] + vs[i] + 1; } else vtt[i] = vtt[i + 1]; } long long say = 100000000000000000; for (long long i = 1; i <= n; i++) { say = min(max(sv[i], vtt[i]), say); } cout << say; } int main() { long long z = 1; while (z--) { solve(); } }