C :

#include<stdio.h>
#include<math.h>
int main()
{
    int a,b,c;
    scanf("%d%d%d",&a,&b,&c);
    int x1=a+b-c,x2=a+c-b,x3=b+c-a,x4=a+b+c;
    double ans=sqrt(x1*x2*x3*x4/16);
    printf("%.2f\n",ans);
    return 0;
}

C++ :

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    float a,b,c,d,s;
    cin>>a>>b>>c;
    {
        d=(a+b+c)/2;
        s=sqrt(d*(d-a)*(d-c)*(d-b));
        cout.precision(2);
        cout.setf(ios::fixed);
        cout<<s<<endl;
    }
    return 0;
}