#include <algorithm>
#include <iostream>
#include <vector>
#include <numeric>
using namespace std;

int main() {
    int n; cin >> n;
    vector<int> a(n);
    for (auto &ai: a) cin >> ai;
    int sum = accumulate(begin(a), end(a), 0);
    int sq = 0;
    while ((sq + 1) * (sq + 1) <= sum) sq++;
    int len = sq * 2 - 1;
    vector<int> b(len);
    for (int i = 0; i < len; i++) b[i] = min(i + 1, len - i);
    if ((int)a.size() < len) a.resize(len);
    for (int i = 0; i < len; i++) sum -= min(a[i], b[i]);
    cout << sum << endl;
    return 0;
}