#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    vector<int> b(n);
    
    int idx = -1;
    for (int i = 0; i < n; i++) {
        cin >> b[i];
        if (b[i] != 0 && idx == -1) {
            idx = i;
        }
    }

    ll ans = 0;
    for (int i = 0; i < n; i++) {
        ans += abs(idx - i);
        b[idx]--;
        if (b[idx] == 0) {
            while (++idx < n) {
                if (b[idx] > 0) break;
            }
        }
        b[i]++;
        if (idx == n) break;
    }
    cout << ans << "\n";
    return 0;
}