#include<bits/stdc++.h>
using namespace std;

#define int long long

typedef long long ll;
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ln <<endl
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
template<class T,class U>void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>void chmax(T &t,U f){if(t<f)t=f;}

int N,M;

int gcd(int a,int b){
    return b?gcd(b,a%b):a;
}

int cnt(int m,int p){
    int ret=0;
    for(;m%p==0;ret++,m/=p);
    return ret;
}

signed main(){
    cin>>N>>M;
    int g=gcd(N,M);
    N/=g;M/=g;

    int tmp=M;
    while(tmp%2==0)tmp/=2;
    while(tmp%5==0)tmp/=5;
    if(tmp!=1){
        cout<<-1<<endl;
        return 0;
    }

    int a=cnt(M,2),b=cnt(M,5);
    int c=1;
    if(a<b)rep(i,b-a)(c*=2)%=10;
    else if(b<a)rep(i,a-b)(c*=5)%=10;

    while(N%10==0)N/=10;
    cout<<N%10*c%10<<endl;
    return 0;
}