#include <iostream>

using namespace std;

struct point{
int x; int y;};

int main()
{
    double p, q, r;
    cin>>p>>q>>r;

    if(p!=r){cout<<"0\n"; return 0;}

    // 2*p*(p+q)
    double ans = 2*p*(p+q);


    unsigned long int ians = ans;
    char afterdot[4];
    ans-=ians;

    ans*=10;
    afterdot[0]='0'+ans;
    ans-=(int)ans;
    ans*=10;
    afterdot[1]='0'+ans;
    ans-=(int)ans;
    ans*=10;
    afterdot[2]='0'+ans;
    ans-=(int)ans;
    ans*=10;
    afterdot[3]='0'+ans;
    ans-=(int)ans;


    cout<<ians<<'.'<<afterdot[0]<<afterdot[1]<<afterdot[2]<<afterdot[3]<<endl;
    return 0;
}
