/*
TASK:abcd
LANG:C++
*/
#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;
typedef long double ld;
ld p,q,r;
int main(){
  cin>>p>>q>>r;
  if(p>r)swap(p,r);
  double ans;
  if(p*p*(q+r) == p*p*(q+p) + p*p*(p-r))ans=(double)((q+r)*2.0*p);
  else{
   if(p==r)ans=-1;
   else{
    ld X=sqrt((p*p*(q+r) - p*p*(q+p))/(p-r));
    ans=(q+r)*((p*p)/X + X);
       }
      }
  if(ans>=0.0)printf("%.4lf\n",ans);
  else printf("0\n");
  return 0;
}
