#include <iostream>
#include <sstream>
#include <algorithm>

using namespace std;

int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }

int calc(int N, int D) {
	int ans = 0;
	if (D > 0) {
		int c = N / D;
		int d = c * D;
		if (gcd(N, d) > 1) {
			N = c;
		}
		ans = N - 1;
	}
	return ans;
}

int main(int argc, char *argv[])
{
	int N, D;
	cin >> N >> D;
	D %= N;
	int ans = max(calc(N, D), calc(N, N - D));
	cout << ans << endl;
	return 0;
}