/**
 * @author: XiaFan
 * @date: 2023-03-08 14:01
 **/
#include <bits/stdc++.h>
using i64 = long long;

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

    int n;
    std::cin >> n;
    std::vector<i64> a(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> a[i];
    }
    i64 ans = 0;
    for (int i = n - 1; i >= 0; i--) {
        i64 sum = a[i];
        for (int j = i - 1; j >= 0; j--) {
            i64 d = std::min(a[i], a[j]);
            sum += d;
            a[j] -= d;
        }
        ans += sum * (i + 1);
    }

    std::cout << ans << "\n";

    return 0;
}