#1333 trapez

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
float B,b,l,h,d,a,c;
cin>>B>>b>>l;
a=(B-b)/2;
h=l*l-a*a;
h=sqrt(h);
c=a+b;
d=h*h+c*c;
d=sqrt(d);
cout<<d;
return 0;
}