import java.io.*;
import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        long n = sc.nextLong();
        long m = sc.nextLong();
        long gcd = getGCD(n, m);
        n /= gcd;
        m /= gcd;
        long x = m;
        while (x % 5 == 0) {
            x /= 5;
        }
        while (x % 2 == 0) {
            x /= 2;
        }
        if (x > 1) {
            System.out.println(-1);
            return;
        } 
        long ans = 0;
        while (n > 0) {
            ans = n / m;
            n %= m;
            n *= 10;
        }
        while (ans % 10 == 0) {
            ans /= 10;
        }
        System.out.println(ans % 10);
    }
    
    static long getGCD(long x, long y) {
        if (y == 0) {
            return x;
        } else {
            return getGCD(y, x % y);
        }
    }
    
}

class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}