#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
double p,q,r;
double e=1e-10;
int main(){
    scanf("%lf %lf %lf",&p,&q,&r);
    if(fabs(p-r)>e){
                    printf("0\n");
                    system("pause");
                    return 0;
                    }
    double dl=0,dr=1e8;
    double t=p+q+r;
    double m1,n1,m2,n2;
    while(dr-dl>e){
                   double d=(dl+dr)/2.;
                   double f=sqrt(t*t+d*d);
                   double lc1=dl,lc2=dr;
                   double rc1=1e24,rc2=1e24;
                   while(rc1-lc1>e){
                                  double c=(lc1+rc1)/2.;
                                  //cout << lc1 << ' ' << rc1 << ' ' << rc1-lc1 << endl;
                                  double m=(c-dl)*(c-dl)+r*r;
                                  double n=(c*c+(p+q)*(p+q));
                                  double cs=(c*c-m-n)/(-2.*sqrt(m)*sqrt(n));
                                  if(cs>0) rc1=c;
                                  else lc1=c;
                                  }//system("pause");
                   while(rc2-lc2>e){
                                    double c=(lc2+rc2)/2.;
                                    //cout << lc2 << ' ' << rc2 << ' ' << rc2-lc2 << endl;
                                    double m=(c-dr)*(c-dr)+r*r;
                                    double n=(c*c+(p+q)*(p+1));
                                    double cs=(c*c-m-n)/(-2.*sqrt(m)*sqrt(n));
                                    if(cs>0) rc2=c;
                                    else lc2=c;
                                    }
                   double c1=lc1,c2=lc2;
                   m1=(c1-dl)*(c1-dl)+r*r;
                   n1=(c1*c1+(p+q)*(p+q));
                   m2=(c2-dr)*(c2-dr)+r*r;
                   n2=(c2*c2+(p+q)*(p+q));
                   if(m1*n1<m2*n2) dr=d;
                   else dl=d;
                   }
    double s=sqrt(m1*n1)*2.;
    int r1=(int)s*10000;
    double res=r1/10000.;
    double diff=s-res;
    if(diff>=0.00005) res+=0.0001;
    printf("%.4lf\n",res);
    //system("pause");
}
