#include <cstdio>

using namespace std;

int main()
{
    double p,q,r,pq;
    scanf ("%lf%lf%lf",&p,&q,&r);
    if ( p != r ) { printf ("0\n"); return 0; }
    pq = p + q;
    printf("%.4lf\n",2*p*pq);
}
