#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;

int main() {
  int A,L,X;
  
  while(cin>>A>>L>>X) {
    double a = A, l = L, x = X;
    double th = acos(a/(2*l));
    double centM = (a*l*sin(th))/2;
    double ph = acos(l/(l+x));
    double sideM = l*(l+x)*sin(ph)/2;
    printf("%.10f\n", sideM + centM);
  }
  
  return 0;
}