#include <bits/stdc++.h>
using namespace std;
int main(){
	double i[3];
	cin>>i[0]>>i[1]>>i[2];
	sort(i,i+3);
	if(i[0]*i[0]+i[1]*i[1]==i[2]*i[2])printf("%.1f",i[0]*i[1]/2);
	else cout<<"No";
	return 0;
}

/**************************************************************
	Problem: 1047
	User: zhouhongyi
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2076 kb
****************************************************************/