#include <stdio.h>
#include <math.h>
int main(){
 int a,b,c;
 scanf("%d %d %d",&a,&b,&c);
 double p=(double)(a+b+c)/2;
 double san =sqrt((double)p*(p-a)*(p-b)*(p-c));
 printf("%.1lf",san);
 return 0;
}