#include <iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<map>
#include<cstdio>
using namespace std;

int main(){
	int n;
	cin >> n;
	vector<int> A(n);
	int i;
	for ( i = 0; i < n; i++) {
		cin >> A[i];
	}
	int ans = 0;
	for ( i = 0; i < n; i++) {
		int a = 1;
		int b = 1; 
		int c = 1;
		for (int j = n-1; j > 0; j--) {
			a = a * j;
		}
		for (int j = n-1-i; j > 0; j--) {
			b = b* j;
		}
		if (i == 0) {
			c = 1;
		}
		else {
			for (int j = i; j > 0; j--) {
				c = c * j;
			}
		}
		int d = b * c;
		ans += A[i] * a / d;
	}
	cout << ans << endl;
	return 0;
}