#include <iostream>
#include <math.h>
using namespace std;
int main()
{
int n;
double k=1;
cin>>n;
double x[n];
for(int i=0;i<n;i++)
{
cin>>x[i];
}
for(int i=1;i<n;i++)
{
k*=((1/(fabs(x[i-1])+1))+x[i]);
}
cout<<k;
return 0;
}
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