#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);

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

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