func_code_string: #include <bits/stdc++.h>   using namespace std;   const int OO = 0x3f3f3f3f, N = 1e5 + 5, mod = 1e9 + 7;   const double pi = acos(-1), eps = 1e-9;   int n, x, c = 1;   vector<int> v;   long long ans;   int main() {     scanf( %d , &n);     for (int i = 0; i < n; ++i) {       scanf( %d , &x);       if (x >= c) {         while (c < x) {           ans += i - v.back();           ++c;           v.pop_back();         }         ++c;       } else {         v.push_back(i);         ans += c - x - 1;       }     }     printf( %lld , ans);     return 0;   }   