用来保存

/*#include<bits/stdc++.h>
using namespace std;
int main()
{
    int a,b,c,js;
    double s,sum=0,jl;
    cin>>a>>b>>c;
    s=(a+b+c)/2;
    js=s*(s-a)*(s-b)*(s-c);
    int xsqz;
    jl=js;
    xsqz=ceil(js);
    if(js==xsqz)
    {
        sum=a*b/2;
        printf("%.2f",sum);
    }
    else cout<<"No";
}
*/