#include <stdio.h>

void main(){
	int a,b,c,t;
	double s;
	scanf("%d%d%d",&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 / 2.0;
		printf("%.1f",s); 
	}else{
		printf("No"); 
	}
}
/**************************************************************
	Problem: 1047
	User: admin
	Language: C
	Result: Accepted
	Time:12 ms
	Memory:1144 kb
****************************************************************/