边长TM可以是小数，我第一次做没想到（哭

#include <bits/stdc++.h>
using namespace std;

double x1, x2, x3;

double s(double a, double b, double c){
double p = 0.5*(a+b+c);
return sqrt(p*(p-a)(p-b)(p-c));
}

int main(){
cin >> x1 >> x2 >> x3;
printf("%.2lf", s(x1, x2, x3));
return 0;
}