1049

PAT_B_1049

#include<stdio.h>
int main()
{
    int n, i;
    double a, ans = 0;
    scanf("%d", &n);
    for (i = 1; i <= n; i++)
    {
        scanf("%lf", &a);
        ans += (double)(n - i + 1)*i*a;
    }
    printf("%.2lf\n", ans);
    system("pause");

    return 0;
}