#include<bits/stdc++.h>
#define int long long
using namespace std;
int a[10005];
signed main() 
{
	cin>>a[0]>>a[1]>>a[2];
	sort(a,a+3);
	if(a[0]*a[0]+a[1]*a[1]==a[2]*a[2])cout<<a[0]*a[1]/2.0;
	else cout<<"no"; 
}