#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#include <unordered_set>
#include <unordered_map>

using namespace std;

#define all(c) ((c).begin()), ((c).end())
#define dump(c) cerr << "> " << #c << " = " << (c) << endl;
#define iter(c) __typeof((c).begin())
#define tr(i, c) for (iter(c) i = (c).begin(); i != (c).end(); i++)
#define REP(i, a, b) for (int i = a; i < (int)(b); i++)
#define rep(i, n) REP(i, 0, n)
#define mp make_pair
#define fst first
#define snd second
#define pb push_back
#define debug(fmt, ...) \
        fprintf( stderr, \
                  fmt "\n", \
                  ##__VA_ARGS__ \
        )

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int INF = 1 << 30;
const double EPS = 1e-10;

double zero(double d) {
    return d < EPS ? 0.0 : d;
}

template<class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool chmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
    return os << '(' << p.first << ',' << p.second << ')';
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &a) {
    os << '[';
    rep(i, a.size()) os << (i ? " " : "") << a[i];
    return os << ']';
}

string toString(int i) {
    stringstream ss;
    ss << i;
    return ss.str();
}

const int MOD = 1000000007;

// a^k
ll fpow(ll a, ll k) {
    ll res = 1ll;
    ll x = a;
    while (k != 0) {
        if ((k & 1) == 1)
            res = (res * x);
        x = (x * x);
        k >>= 1;
    }
    return res;
}

struct prepare {
    prepare() {
        cout.setf(ios::fixed, ios::floatfield);
        cout.precision(8);
        ios_base::sync_with_stdio(false);
    }
} _prepare;

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

int main() {
    ll N, M;
    cin >> N >> M;

    ll d = gcd(N, M);
    N /= d;
    M /= d;

    // 有限か無限か
    int c2 = 0, c5 = 0;
    ll tmpM = M;
    while (tmpM % 2 == 0) tmpM /= 2, c2++;
    while (tmpM % 5 == 0) tmpM /= 5, c5++;
    bool is_lim = (tmpM == 1);

    // 割り切れる
    if(N % M == 0) {
        ll t = N / M;
        while(t % 10 == 0) t /= 10;
        cout << t % 10 << endl;
        return 0;
    }

    if (!is_lim) {
        cout << -1 << endl;
    }
    else {
        int mi = min(c2, c5);
        c2 -= mi;
        c5 -= mi;

        while(N % 10 == 0)
            N /= 10;

        N %= 10;

        if (c2 == 0 && c5 == 0) {
            cout << N << endl;
        } else {
            bool is_c2_bigger = c2 > c5;
            rep(i, max(c2, c5)) {
                if(is_c2_bigger)
                    N *= 5;
                else
                    N *= 2;

                while(N % 10 == 0)
                    N /= 10;

                N %= 10;
            }

            if(N % 10 == 0)
                cout << ((N%100) - (N%10)) / 10 << endl;
            else
                cout << N % 10 << endl;
        }
    }

    return 0;
}