# include<stdio.h>
# include<math.h>
int main(){
    double p,a,b,c,area;
    scanf("%lf",&a);
    scanf("%lf",&b);
    scanf("%lf",&c);
    p = 0.5*(a+b+c);
    area = q*(q-a)*(q-b)*(q-c);
    area = sqrt(area);
    printf("%.1lf",area);
    return 0;
}