#include <bits/stdc++.h>
using namespace std;
int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    int ans = 1 << 30;
    for (int i = 0; i < n; i++) cin >> a[i];
    int SUM = 0;
    for (int i = 0; i < n; i++) SUM += a[i];
    for (int i = 2; i <= 100000; i++) {
        vector<int> p;
        int sum = 0;
        for (int j = 1; j <= i; j++) {
            p.push_back(j);
            sum += j;
        }
        for (int j = i - 1; j >= 1; j--) {
            p.push_back(j);
            sum += j;
        }
        
        if (sum > SUM) {
            cout << ans << endl;
            return 0;
        }
        if (p.size() < a.size()) {
            int x = a.size() - p.size();
            while (x--) {
                p.push_back(0);
            }
        } else {
            int x = p.size() - a.size();
            while (x--) {
                a.push_back(0);
            }
        }
        /*
        for (int i = 0; i < a.size(); i++) cout << a[i] << " ";
        cout << endl;
        for (int i = 0; i < p.size(); i++) cout << p[i] << " ";
        cout << endl;
        */
        int cost = 0;
        for (int i = 0; i < a.size(); i++) {
            if (a[i] - p[i] > 0) {
                cost += a[i] - p[i];
            }
        }
        ans = min(ans , cost);
    }
    cout << ans << endl;
    return 0;
}