#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a,b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define spair(p) cout<<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout<<" "<<kbrni;cout<<endl
#define smap(m) cout<<#m<<":";each(kbrni,m)cout<<" {"<<kbrni.first<<":"<<kbrni.second<<"}";cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100005;

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

int res(ll u)
{
    while(u){
        if(u % 10 != 0){
            return u % 10;
        }
        u /= 10;
    }
}

int res2(ll a,ll b,ll c)
{
    rep(i,c){
        a *= b;
        a %= 10;
    }
    return a;
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll n,m;
    cin >> n >> m;
    if(n % m == 0){
        cout << res(n/m) << endl;
        return 0;
    }
    ll g = gcd(n,m);
    n /= g,m /= g;
    int two = 0,five = 0;
    while(1){
        if(m % 2 != 0){
            break;
        }
        m /= 2;
        two++;
    }
    while(1){
        if(m % 5 != 0){
            break;
        }
        m /= 5;
        five++;
    }
    if(m != 1){
        cout << "-1\n";
        return 0;
    }
    if(two >= five){
        cout << res2(n%10,5,two-five) << endl;
    }else{
        cout << res2(n%10,2,five-two) << endl;
    }
    return 0;
}