#include <bits/stdc++.h> using namespace std; int n, ans, a[1005]; int main() { cin >> n; for (int i = 1; i <= n; i++) cin >> a[i]; for (int i = 1; i <= n; i++) { for (int j = i + 1; j <= n; j++) { for (int k = j + 1; k <= n; k++) { ans += a[i] + a[j] + a[k]; } } } cout << ans << endl; return 0; }