// yukicoder: No.25 有限小数
// 2019.4.8 bal4u
// 有限小数の条件と求め方

#include <stdio.h>

int check(long long x)
{
	while ((x & 1) == 0) x >>= 1;
	while (x % 5 == 0) x /= 5;
	return x == 1;
}

int main()
{
	int ans;
	long long N, M;
	scanf("%lld%lld", &N, &M);
	if (!check(M)) ans = -1;
	else {
		if ((ans = (int)(N % M)) == 0) {
			N /= M;	while ((ans = (int)(N % 10)) == 0) N /= 10;
		}
		else {
			N %= M;
			while (N % M) {
				N -= (N / M) * M;
				while (N < M) N *= 10;
			}
			ans = (int)(N / M);
		}
	}
	printf("%d\n", ans);
	return 0;
}