#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c;
    float n;
    cin>>a>>b>>c;
    if(a>b&&b>c&&c*c+b*b==a*a){
    	n=c*b/2.0;
    	printf("%.1f",n);	
    }if(a>c&&c>b&&c*c+b*b==a*a){
    	n=c*b/2.0;
    	printf("%.1f",n);
    }if(b>a&&a>c&&a*a+c*c==b*b){
    	n=c*a/2.0;
    	printf("%.1f",n);
    }if(b>c&&c>a&&c*c+a*a==b*b){
    	n=c*a/2.0;
    	printf("%.1f",n);
    }if(c>a&&a>b&&a*a+b*b==c*c){
    	n=b*a/2.0;
    	printf("%.1f",n);
    }if(c>b&&b>a&&b*b+a*a==c*c){
    	n=b*a/2.0;
    	printf("%.1f",n);
    }else{
    	cout<<"No";
    }
}
/**************************************************************
	Problem: 1047
	User: sucongyi
	Language: C++
	Result: Wrong Answer
****************************************************************/