//#include <bits/stdc++.h>
#include <assert.h>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <iterator>
using namespace std;

typedef signed long long ll;

#define pp(...) (void)printf(__VA_ARGS__)
#define For(x,to) for(x=0;x<(to);x++)
#define ForAuto(x,arr) for(auto& x:arr)
#define ForBeginEnd(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define All(a) (a.begin()),(a.end())
#define Zeros(a) memset(a,0,sizeof(a))
#define Minus(a) memset(a,0xff,sizeof(a))

#define PI 3.14159265
#define EPS (1e-10)
#define EPS_eq(a,b) (abs((a)-(b)) < EPS)

#pragma GCC diagnostic ignored "-Wconversion"

//#define int long long
const int INF = 1000*1000;

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

typedef pair<int, int> P;

void pp_int(int x){ printf("%d\n", x); };

//-------------------------------------------------

signed main() {
    ll n,m;cin>>n>>m;

    ll gcd = __gcd(n,m);
    n /= gcd;
    m /= gcd;

    if(n % m == 0){
        ll res = n/m;
        while(res % 10 == 0){
            res /= 10;
        }
        printf("%lld\n", res % 10);
        return 0;
    }

    ll m5 = 0, m2 = 0;
    while(m % 2 == 0) m /= 2, m2++;
    while(m % 5 == 0) m /= 5, m5++;

    if (m != 1) {
        printf("-1\n");
        return 0;
    }

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

    while(m2 > m5){
        m5++;
        n *= 5;
        while(n % 10==0)n/=10;
    }
    while(m2 < m5){
        m2++;
        n *= 2;
        while(n % 10==0)n/=10;
    }

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

    printf("%lld\n", n % 10);

    return 0;
}