A1104 Sum of Number Segments [连续子序列分割]

#include<iostream>
#include<cstdio>
using namespace std;
int main() {
	int n;
	cin >> n;
	long double val, sum = 0.0;
	for (int i = 1; i <= n; i++) {
		cin >> val;
		sum += val * (n - i + 1) * i;
	}
	printf("%.2lf", sum);
	return 0;
}