#include <stdio.h>
#include <string.h>

void swap(long long int *a, long long int *b)
{
	long long int temp;
	temp = *a;
	*a = *b;
	*b = temp;
}

int lcm(long long int m, long long int n)
{
	long long int temp;
	
	if(m < n)swap(m, n);
	while(n != 0){
		temp = n;
		n = m % n;
		m = temp;
	}

	return m;
}


int main(void) {
	int i;
	int pos;
	int foot[20] = {0};
	long long int n, d;
	int cnt;
	
	/*
	for(n = 1;n < 10;n++){
		for(d = 1;d <= n;d++){
			printf("n = %lld, d = %lld : ", n, d);
			memset(foot, (int)0, sizeof(foot));
			pos = 1;
			cnt = 0;
			while(foot[pos] != 1){
				printf("%d ", pos);
				foot[pos] = 1;
				cnt++;
				pos = (pos - 1 + d) % n + 1;
			}
			
			printf(" %d times\n", cnt - 1);
		}
		printf("\n");
	}
	*/	
	//lcm(8, 6);
	
	scanf("%lld%lld", &n, &d);
	if(n == d)printf("0\n");
	else if(d == 1 || n - 1 == d)printf("%lld\n", n - 1);
	else if(lcm(n, d) == 1)printf("%lld\n", n - 1);
	else {
		printf("%lld\n", n / lcm(n, d) - 1);
	}
	
	return 0;
}