新手刷题

#include<bits/stdc++.h>
using namespace std;
double mianji(double a,double b,double c)
{
    double p = (a+b+c)/2.0;
    return sqrt(p*(p-a)*(p-b)*(p-c));
}
int main()
{
    double a,b,c;
    cin>>a>>b>>c;
    printf("%.2f",mianji(a,b,c));
    return 0;
}