#include <stdio.h>
#include <math.h>
int main (void){
	int a,b,res;
	scanf("%d %d",&a,&b);
	if(a>0){b=(-1)*b;
		if(b>0){
				if(abs(b)%2==0){a=(-1)*a;}
	}
		else{
			if(abs(b)%2!=0){a=(-1)*a;}
		}
	}
	else{b=2*b;
		if(b>0){
				if(abs(b)%2!=0){a=(-1)*a;}
	}
		else{
			if(abs(b)%2==0){a=(-1)*a;}
		}
	}

	res=a-b;
	printf("%d\n",res);
	
	return 0;
}