#include<stdio.h>
#include<math.h>
#include<algorithm>
using namespace std;

#define inf 1999888777
#define eps 0.000001
#define pi 3.14159265358979


int main() {

     double a,d,ab,bc,cd,bd,res;
	 scanf("%lf %lf %lf", &ab, &bc, &cd);

	 if ( fabs(ab-cd) < eps ) {

	   a=ab;
	   bd=bc+cd;
	   d=bd;

	   res=( sqrt(a*a + ab*ab) * sqrt(d*d + bd*bd) );
	   printf("%.4lf\n", res);

	 } else printf("0\n");

     return 0;
}