C++ :

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

Python :

# coding=utf-8
a=int(input())
b=int(input())
c=int(input())
if a*a+b*b==c*c:
    print(int(a*b/2))
elif a*a+c*c==b*b:
    print(int(a*c/2))
elif b*b+c*c==a*a:
    print(int(b*c/2))
else:
    print('no')