#include <iostream>
#include <cstdio>
#include <cmath>
#define s2 sqrt(2)
using namespace std;

double a,b,c;
double ans;
int main ()
{
    cin>>a>>b>>c;
    if (a!=c) cout<<0<<endl;

    else {
            ans=(a+b)*s2*s2*c;
          cout<<int(ans)<<".0000"<<endl;

            }

    }
