#include <iostream>
using namespace std;

const int MAX_N = 110;
int a[MAX_N];

int int_pow(int a, int b) {
    int res = 1;
    for (int i = 0; i < b; i++) res *= a;
    return res;
}

int main() {
    int n, sum = 0;
    cin >> n;

    for (int i = 0; i < n; i++) {
        cin >> a[i];
        sum += a[i];
    }

    int ans = (1 << 28);
    for (int w = (n % 2 == 1) ? n : (n - 1); w >= 1; w -= 2) {
        int use_block = int_pow((w + 1) / 2, 2);
        if (use_block > sum) continue;

        for (int left_end = 0; left_end + w <= n; left_end++) {
            int cost = 0, missing = 0;
            for (int b_i = 0; b_i < n; b_i++) {
                if (b_i < left_end || b_i >= left_end + w) {
                    // 全部削る
                    cost += a[b_i];
                } else {
                    int block_h = min(b_i, n - b_i - 1) + 1;
                    cost += abs(a[b_i] - block_h);
                    if (a[b_i] < block_h) missing += block_h - a[b_i];
                }
            }
            ans = min(ans, cost - missing);
        }
    }
    cout << ans << endl;

    return 0;
}