#include "bits/stdc++.h"
using namespace std;
int main(){
	int N,ans=0;
	cin >> N;
	vector<int> A(N);
	int sum = 0;
	for (int i = 0; i < N; i++)
	{
		cin >> A[i];
		sum += A[i];
	}
	int target = (int)sqrt(sum + 0.1);//誤差なくす。
	for (int i = 0; i < N; i++)
	{
		ans += max(0, A[i] - target - abs((target - 1) - i));
	}
	cout << ans << endl;
}