#include <iostream>
using namespace std;
int a[250000000];
int main(void) {
	int N, D, count = 0;
	cin.tie(0);
	cin >> N >> D;
	a[0] = a[1] = 1;
	for (int i = 1+D;; i+=D) {
		if (i <= N) {
			if(!a[i]) {
				count++;
				a[i] = 1;
			} else {
				break;
			}
		} else {
			i-=N;
			if(!a[i]) {
				count++;
				a[i] = 1;
			} else {
				break;
			}
		}
	}
	cout <<count<<endl;
	return 0;
}