#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
 
int main() {
 
    double a,ans = 0;
    double b;
    double c=0.0;
    scanf("%lf %lf",&a,&b);
    while((a+b)-0.01>c)
    {
        if(a+b-0.01>c && b+c-0.01>a && c+a-0.01>b)
        {
            double s = (a+b+c)/2.0;
            double area= sqrt(s*(s-a)*(s-b)*(s-c));
            if(area>= ans)
            {
                ans = area;
            }
        }
 
 
        c+= 0.01;
    }
    printf("%.2lf\n",ans);
    return 0;
}
 

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