#include <iostream>
#include <vector>

using namespace std;
#define rep(i, a, b) for(int i = a; i < b; i++)

int main(void)
{
	int i, j, n, tmp, sum=0, size;
	vector<int> a, b;
	cin >> n;
	rep(i, 0, n) {
		cin >> tmp;
		a.push_back(tmp);
		sum += tmp;
	}

	// aから完成形bの要素を調べる
	int height = 0;
	for (size = 0, j = 1; size + j <= sum; j += 2) {
		size += j;
		height++;
	}
	int width = j - 2;

	// aとbを整形する 
	while (a.size() < width) {
		a.push_back(0);
	}
	while (b.size() < width) {
		b.push_back(0);
	}
	int as = a.size(), bs = b.size();

	for (i = 0, j = 1; i < width; i++) {
		b[i] = j;
		if (i < width / 2) {
			j++;
		} else {
			j--;
		}
	}

	int x = 0;
	rep(i, 0, as) {
		if (i < bs) {
			if (a[i] > b[i]) x += a[i] - b[i];
		} else {
			x += a[i];
		}
	}
	cout << x << endl;
}