1104. Sum of Number Segments (20)

#include <iostream>

using namespace std;

double num[100010];

int main()
{
	int n;
	scanf("%d", &n);

	int i;
	for(i = 1; i <= n; i++)
	{
		scanf("%lf", &num[i]);
	}

	double res = 0;
	for(i = 1; i <= n; i++)
	{
		res += num[i] * i * (n + 1 - i);
	}

	printf("%.2lf\n", res);

	system("pause");
	return 0;
}