#include<stdio.h>
#include<math.h>
int main(){
	int a,b,c,m,n;
	scanf("%d %d",&a,&b);
	m = abs(a);
	n = abs(b);
	if(a > 0){
      b = -b;
    }else{
      b = 2*b;
	}
      if(n % 2 !=0){
      	if(b < 0){
      		a = -a;
        }else{
        	a = a;
		}
	  }else{
	  	if(b > 0){
	  		a = -a;
		  }else{
		  	a = a;
		  }
	  }
	  c = a - b;
	printf("%d\n",c);
	return 0;
}