题解

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