#include <iostream>
#include <cstdio>
#include <cmath>

using namespace std;

#define DELTA 0.00001
#define MAX 1000000000.0

class Point {
  public:
    double x, y;
    
    Point() {
      x = y = MAX;
    }
    
    Point(double _x, double _y) {
      x = _x;
      y = _y;
    }
};

class Line {
  
  public:
    
    Point a, b;
    
    Line() {
      a = b = Point();
    }
    
    Line(Point _a,Point _b) {
      a = _a;
      b = _b;
    }
    
    double operator^(Line l) {
      return dx()*l.dy() - dy()*l.dx();
    }
    
  private:
    double dx() {
      return b.x-a.x;
    }
    
    double dy() {
      return b.y-a.y;
    }
};

bool eq(double a, double b) {
  return abs(a-b) < DELTA;
}

int main() {  
  double p, q, r;
  
  bool no_result = true;
  
  cin>>p>>q>>r;
  
  Point A(0,0), B(p, 0), C(p+q, 0), D(p+q+r, 0);
  
  if(eq(p, r)) {
    B.y = -p;
    C.y = p + q;
    printf("%.4f\n", abs(Line(A,B)^Line(A,C)));
  }  
  else {
  
    cout<<0;
  
  }
  
  return 0;
}