#include <iostream>

using namespace std;
int main()
{

int i,br=0;
float s;
int niz[100];
i=0;
s=0;
do
{cin>>niz[i];
s=s+niz[i];
br++;
}
while(niz[i]>0);
i++;
cout<<s/(br-1)<<endl;

return 0;
}