题解

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