PAT-A1104

#include<stdio.h> int main(){ int i, j, n; double ans=0,d[100010]={0}; scanf("%d",&n); for(i=1;i<=n;i++){ scanf("%lf",&d[i]); ans=ans+d[i]*i*(n-i+1); } printf("%0.2f\n",ans); return 0; }