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

typedef long long ll;
typedef vector< int > vi;
typedef vector< vi > vvi;
typedef vector< ll > vl;
typedef vector< vl > vvl;
typedef pair< int, int > pii;
typedef vector< pii > vp;
typedef vector< double > vd;
typedef vector< vd > vvd;
typedef vector< string > vs;

template< class T1, class T2 >
int upmin( T1 &x, T2 v ){
  if( x > v ){
    x = v;
    return 1;
  }
  return 0;
}

template< class T1, class T2 >
int upmax( T1 &x, T2 v ){
  if( x < v ){
    x = v;
    return 1;
  }
  return 0;
}

const int INF = 0x3f3f3f3f;
ll N, M;

void init(){
  cin >> N >> M;
}

void preprocess(){
  ll g = __gcd( N, M );
  N /= g, M /= g;
}

void solve(){
  while( N % 10 == 0 )
    N /= 10;
  if( M == 1 )
    cout << N % 10 << endl, exit( 0 );
  int cnt2 = 0, cnt5 = 0;
  while( M % 2 == 0 )
    M /= 2,
    ++cnt2;
  while( M % 5 == 0 )
    M /= 5,
    ++cnt5;
  if( M > 1 )
    cout << -1 << endl, exit( 0 );
  int cnt10 = min( cnt2, cnt5 );
  cnt2 -= cnt10, cnt5 -= cnt10;
  if( cnt2 ){
    int v = N % 10;
    for( int i = 0; i < cnt2; ++i )
      v = v * 10 / 2 % 10;
    cout << v << endl;
  } else if( cnt5 ){
    int v = N % 10;
    for( int i = 0; i < cnt5; ++i )
      v = v * 10 / 5 % 10;
    cout << v << endl;
  } else{
    cout << N % 10 << endl;
  }
}

signed main(){
  ios::sync_with_stdio( 0 );
  init();
  preprocess();
  solve();
  return 0;
}