#include<iostream>
#include <iomanip>
using namespace std;
int main(){
	int a,b,c,t;
	double s;//面积
	cin>>a>>b>>c;
	if(a>b){
		t=a;
		a=b;
		b=t;
		
	}
	if(b>c){
		t=b;
		b=c;
		c=t;
	}

	
	if(a*a+b*b==c*c){
		s = a * b * 1.0 / 2;
		cout<<fixed<<setprecision(1)<<s<<endl;
		
	}else{
		cout<<"No"<<endl;
	}
}

/**************************************************************
	Problem: 1047
	User: admin
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/