import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;

T gcd(T)(T a, T b) {
    if (b == 0) return a;
    return gcd(b, a % b);
}

int calc(long n, long m) {
    long g = gcd(n, m);
    n /= g;
    m /= g;

    int d2 = 0;
    int d5 = 0;
    while (m % 2 == 0) { d2++; m /= 2; }
    while (m % 5 == 0) { d5++; m /= 5; }

    if (m != 1) return -1;

    while (d2 < d5) { d2++; n *= 2; }
    while (d5 < d2) { d5++; n *= 5; }

    while (n % 10 == 0) n /= 10;
    return n % 10;
}

void main() {
    long n = read!long;
    long m = read!long;
    auto ans = calc(n, m);
    writeln(ans);
}