题解

#include <bits/stdc++.h>
using namespace std;
double a,b,c,p;
double s;
int main(){
	cin>>a>>b>>c;
    p=(a+b+c)/2;
    s=sqrt(p*(p-a)*(p-b)*(p-c));
    printf("%.2f",s);
	return 0;
 }