#include <iostream>

#define LL long long

using namespace std;

const LL MAX = 2000000000;

int countPattern(LL left, LL center)
{
	LL right_count = 0;
	if(left < center) {
		
		// 13(2) : x = 1 ~ 3 ... (center - left - 1) 通り
		right_count += center - left - 1;
		
		// 23(1) : x < 2 ... left == 1 ... 0通り, left != 1 ... (left - 1) 通り
		if(left != 1) {
			right_count += left - 1;
		}
		
	} else {
		
		// 21(3) : x = 2 ~ MAX ... (MAX - left) 通り
		right_count += MAX - left;
		
		// 31(2) : x = 1 ~ 3 ... (left - center - 1) 通り
		if(left - center > 1){
			right_count += left - center - 1;
		}
	}
	
	return right_count;
}

int main()
{
	LL left = 0;
	LL center = 0;
	
	cin >> left >> center;
	
	cout << countPattern(left, center) << endl;
	
	return 0;
}