#include<cstdio>
#include<cmath>
#define pi 3.141592654
using namespace std;
double reldist(double ax,double ay,double bx,double by)
{
    return (ax-bx)*(ax-bx)+(ay-by)*(ay-by);
}
double dist(double ax,double ay,double bx,double by)
{
    return sqrt((ax-bx)*(ax-bx)+(ay-by)*(ay-by));
}
int main()
{
    double p,q,r,a1x,a1y,a2x,a2y,b1x,b1y,b2x,b2y,c1x,c1y,c2x,c2y,d1x,d1y,d2x,d2y;
    double t,t1,t2=-1.0;
    double x,y;
    double ang;
    scanf("%lf %lf %lf",&p,&q,&r);
    for(double i=0.002;i<90;i+=0.002)
    {
        ang=tan(i*pi/180);
        x=0;y=0;
        y+=ang*(p+q);
        x+=p+q;
        c1x=x;c1y=y;
        y-=(r/ang);
        x+=r;
        d1x=x;d1y=y;
        y-=ang*(q+r);
        x-=(q+r);
        b1x=x;b1y=y;
        y+=p/ang;
        x-=p;
        a1x=x;a1y=y;
        if(a1y<0+1e-9&&a1y>0-1e-9)
        {
            t=reldist(a1x,a1y,c1x,c1y);
            t1=reldist(d1x,d1y,b1x,b1y);
            if(t<t1+1e-9&&t>t1-1e-9)
            {
                t=reldist(a1x,a1y,b1x,b1y);
                t1=reldist(d1x,d1y,c1x,c1y);
                if(t<t1+1e-9&&t>t1-1e-9)
                {
                    t=dist(a1x,a1y,b1x,b1y)*dist(a1x,a1y,c1x,c1y);
                    if(t<t2||t2==-1.0) t2=t;
                }
            }
        }
        x=0;y=0;
        y+=ang*p;
        x+=p;
        b1x=x;b1y=y;
        y-=((r+q)/ang);
        x+=r+q;
        d1x=x;d1y=y;
        y-=ang*r;
        x-=r;
        c1x=x;c1y=y;
        y+=(p+q)/ang;
        x-=(p+q);
        a1x=x;a1y=y;
        if(a1y<0+1e-9&&a1y>0-1e-9)
        {
            t=reldist(a1x,a1y,c1x,c1y);
            t1=reldist(d1x,d1y,b1x,b1y);
            if(t<t1+1e-9&&t>t1-1e-9)
            {
                t=reldist(a1x,a1y,b1x,b1y);
                t1=reldist(d1x,d1y,c1x,c1y);
                if(t<t1+1e-9&&t>t1-1e-9)
                {
                    t=dist(a1x,a1y,b1x,b1y)*dist(a1x,a1y,c1x,c1y);
                    if(t>0)
                    if(t<t2||t2==-1.0) t2=t;
                }
            }
        }
    }
    printf("%.4lf\n",t2);
}
