#include <iostream>
#include <cmath>
using namespace std;


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int N, A[110], block_total = 0;
    cin >> N;
    for (int i = 0; i < N; i++) {
        cin >> A[i];
        block_total += A[i];
    }
    int max_cols = (int)sqrt(block_total);

    int ans = block_total;
    for (int i = 1; i <= max_cols; i++) {
        int surplus = 0, h = 1, dh = 1, j = 0;
        for (; j < 2*i-1; j++, h+=dh) {
            surplus += max(0, A[j]-h);
            if (j == i-1) dh = -1;
        }
        for (; j < N; j++) {
            surplus += A[j];
        }
        ans = min(ans, surplus);
    }

    cout << ans << endl;

    
    return 0;
}