#include <bits/stdc++.h>
using namespace std;
long long gcd(long long x,long long y){
    long long r;
    while(x){
        r=y; y=x; x=r%x;
    }
    return y;
}
int main(){
    int i, j, k;
    int p2 = 0, p5 = 0;
    long long n,m,g;

    scanf("%lld %lld",&n,&m);
    g=gcd(n,m);
    n/=g; m/=g;

    while(m%2==0) m/=2,p2++;
    while(m%5==0) m/=5,p5++;
    if(m>1){
        printf("-1");
        return 0;
    }

    while(n%10==0) n/=10;
    n%=10;
    while(p2>p5) p5++,n=(n*5)%10;
    while(p2<p5) p2++,n=(n*2)%10;

    printf("%d\n",(int)n);
    return 0;
}