#include<iostream>
#include<fstream>
#include<math.h>
#include<vector>
#include <array>
#include <algorithm>
#include <queue>
#include <numeric>
#include <map>
#include <climits>

using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) //printf(__VA_ARGS__)

typedef pair<int, int> pos;
int pos::*x = &pos::first;
int pos::*y = &pos::second;

int dxy[] = {0, 1, 0, -1, 0};

int gcd(int a, int b) {
    if(a<b){
        int tmp = a;
        a = b;
        b = tmp;
    }
    int r = a % b;
    while(r!=0){
        a = b;
        b = r;
        r = a % b;
    }
    return b;
}

/*================================*/

int N, M;
int A[20], B[20];

signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    
    cin >> N >> M;
    
    int g = gcd(N, M);

    out("%lld, %lld\n", N, M);
    out("%lld\n", g);
    
    N /= g;
    M /= g;
    N %= 10;
    
    while (M % 2 == 0) {
        M /= 2;
        N *= 5;
    }
    while (M % 5 == 0) {
        M /= 5;
        N *= 2;
    }
    if (M != 1) {
        cout << -1 << endl;
        return 0;
    }
    while (N % 10 == 0) N /= 10;
    
    cout << N % 10 << endl;
    
    return 0;
}