#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <functional>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cctype>
#include <string>

using namespace std;

int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  int total = 0;
  for (int i = 0; i < n; i++) total += a[i];
  int cnt = 1;
  for (int i = 1; ; cnt+=2, i++) if (total < i*i) break;
  cnt -= 2;
  int ans = 0;
  for (int i = 0; i < cnt/2 && i < n; i++) ans += max(0, a[i]-(i+1));
  for (int i = cnt/2, j = cnt/2; i < cnt && i < n; i++,j--) ans += max(0, a[i]-(j+1));
  for (int i = cnt; i < n; i++) ans += a[i];

  cout << ans << endl;
}