函数

#include<bits/stdc++.h>
using namespace std;
double p,k;
double san(double a,double b,double c){
	p=(a+b+c)/2.0;
	k=sqrt(p*(p-a)*(p-b)*(p-c));
	return k;
}
int main(){
	double a,b,c;
	cin>>a>>b>>c;
	cout<<fixed<<setprecision(2)<<san(a,b,c);
	return 0; 
}