#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <cstring>

typedef long long ll;
using namespace std;

#define mod 1000003
#define INF 10000000
#define LLINF 2000000000000000000LL

#define SIZE 10000

ll n,m;

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

int main(){
    ll ans=0;
    
    cin >> n >> m;
    
    ll G = gcd(n,m);
    n/=G;
    m/=G;
    
    if(m==1){
        while(n%10==0) n/=10;
        printf("%lld\n",n%10);
        return 0;
    }
    
    ll M = m;
    bool M2=false,M5=false;
    
    while(M%2==0){ M/=2; M2=true;}
    while(M%5==0){ M/=5; M5=true;}
    
    if(M!=1){
        puts("-1");
        return 0;
    }
    
    if(m<(1LL<<55)){
        
        while(n%m>0){
            n%=m;
            n*=10;
        }
        
        printf("%lld\n",n/m);
        return 0;
    }
    
    if((M2 && M5) || m<(1LL<<55)){
        m/=10;
        
        while(n%m>0){
            n%=m;
            n*=10;
        }
        
        printf("%lld\n",n/m);
        return 0;
    }
    
    if(M5){
        m/=25;
        
        while(n%m>0){
            ans*=10;
            ans+=n/m;
            ans%=1000;
            n%=m;
            n*=10;
        }
        ans*=10;
        ans+=n/m;
        
        while(ans%25>0){
            ans%=25;
            ans*=10;
        }
        
        printf("%lld\n",(ans/25)%10);
    }
    
    if(M2){
        m/=16;
        
        while(n%m>0){
            ans*=10;
            ans+=n/m;
            ans%=1000;
            n%=m;
            n*=10;
        }
        
        while(ans%16>0){
            ans%=16;
            ans*=10;
        }
        
        printf("%lld\n",(ans/16)%10);
    }
    
    return 0;
}