题解

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