#include <bits/stdc++.h>
using namespace std;

using ll = long long;
#define rep(i, n) for(ll i = 0; i < n; i++)

int main() {
	int N;
	cin >> N;
	int ma = 8;
	vector<ll> v(ma + 1);
	rep(i, N) {
		int a;
		cin >> a;
		v[a]++;
	}
	ll ans = 0;
	rep(i, ma + 1) {
		if(v[i] == 0) continue;
		rep(j, ma + 1) {
			if(v[j] == 0) continue;
			ll p = pow(i, j);
			ans += p * v[i] * v[j];
		}
	}
	cout << ans << endl;
}