C++ :

#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c;
    cin>>a>>b>>c;
    if(a*a+b*b==c*c)
    cout<<a*b/2;
    else if(a*a+c*c==b*b)
    cout<<a*c/2;
    else if(c*c+b*b==a*a)
    cout<<b*c/2;
    else cout<<"no";
    return 0;
} 

Python :

# coding=utf-8
x=int(input())
y=int(input())
z=int(input())
if x*x==z*z+y*y:
    print(round(z*y/2))
elif z*z==x*x+y*y:
    print(round(x*y/2))
elif y*y==x*x+z*z:
    print(round(x*z/2))
else:
    print("no")