#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c;
    cin>>a>>b>>c;
    if(a<b) swap(a,b);
    if(a<c) swap(a,c);
    if(b<c) swap(b,c);
    if(b*b+c*c==a*a){
        printf("%.1f",b*c/2.0); 
    }else{
        cout<<"No";
    }
    return 0;
} 
/**************************************************************
	Problem: 1047
	User: panjinyan
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/