import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long M = sc.nextLong();
        long gcd = gcd(N,M);
        N/=gcd;
        M/=gcd;
        long ans = ans(N,M);
        System.out.println(ans);
    }
    static long gcd(long x, long y){
        while(true){
            long z=x%y;
            if(z==0){break;}
            x=y;
            y=z;
        }
        return y;
    }
    static int ans(long N, long M){
        long t=M;
        while(t%2==0){
            t/=2;
        }
        while(t%5==0){
            t/=5;
        }
        int r=-1;
        if(t==1){
            BigDecimal x = new BigDecimal(N);
            BigDecimal y = new BigDecimal(M);
            BigDecimal z = x.divide(y, 1000, BigDecimal.ROUND_UNNECESSARY);
            String w = z.toPlainString();
            for(int i=w.length()-1; i>=0; i--){
                int A = w.charAt(i);
                if(A!='0'&&A!='.'){
                    r=w.charAt(i)-'0';
                    break;
                }
            }
        }
        return r;
    }
}