#include<bits/stdc++.h>
using namespace std;
long double F,l,x;
int n;
int main(){
cin>>n;
for(int i=1;i<=n;++i)
cin>>x,l=(l+1)*x,F+=l*2-x;
printf("%.10Lf",F);
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1092. Shortest Common Supersequence | 1044. Longest Duplicate Substring |
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Zoos | Build a graph |