#include <cstdlib>
#include <cstdio>
#include <cmath>
#define EPS (1e-10)
using namespace std;

double a, b, c;

inline void impossible ()
{
    int A = (a + EPS)*100;
    int C = (c + EPS)*100;

    if (A != C)
    {
        printf ("0\n");
        exit (0);
    }
}

inline void read ()
{
    scanf ("%lf %lf %lf", &a, &b, &c);
    impossible ();
}

int main ()
{
    read ();
    printf ("%.4lf\n", 2. * a * (a + b));
    return 0;
}
