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

#define SQ(A) ((A)*(A))

float p,q,r;

double AC(double d)
{
    return 2*SQ(d)-2*d*sqrt(SQ(d)-q*p-SQ(p)) - q*p;
}

double BC(double d)
{
    return 2*SQ(d)+2*d*sqrt(SQ(d)-q*p-SQ(p)) + q*p + SQ(q);
}

double Area(double d)
{
    return sqrt(AC(d) * BC(d));
}

int main()
{
    scanf("%f %f %f", &p, &q, &r);

    if(p!=r)
        printf("0\n");
    else
        printf("%.4f\n", Area(p+q/2));


    return 0;
}
