#include<stdio.h>
int main(){
   int a,b;
   int P_a,P_b;
   int result;
   float n;
   scanf("%d%d",&a,&b);
   if(a>0){
   	P_b=-1*b;
   }
   if(a<=0){
   	P_b=2*b;
   }
   n=P_b%2;
   if(n!=0){
   	if(a*P_b>0){
   		P_a=a;
	   }
	if(a*P_b<0){
		P_a=-1*a;
	}
   }
   if(n==0){
   	if(a*P_b>0){
   		P_a=-1*a;
	   }
	if(a*P_b<0){
		P_a=a;   	
   }
}
   result=P_a-P_b;
   printf("%d",result);
}