#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,b,c;
	float s;
	cin>>a>>b>>c;
	if(a<b)swap(a,b);
	if(a<c)swap(a,c);
	if(b<c)swap(b,c);
	if((c*c+b*b)==(a*a)){
		s=0.5*b*c;
		printf("%.1f",s);
	}else {
		cout<<"No";
	}
	return 0;
}

/**************************************************************
	Problem: 1047
	User: tangkaixuan
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/