#include<stdio.h>
#include<stdlib.h>

typedef long long int ln;

ln gcd(ln n,ln m){
  ln r=n%m;
  while(r!=0){
    n=m;
    m=r;
    r=n%m;
  }
  return m;
}

int isFinite(ln m){
  while(m%2==0){
    m/=2;
  }
  while(m%5==0){
    m/=5;
  }
  return m==1;
}

void run(void){
  ln n,m;
  scanf("%lld%lld",&n,&m);

  ln r=gcd(n,m);
  n/=r;
  m/=r;
  if(!isFinite(m)){
    printf("-1\n");
    return;
  }

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

  while(m%10==0){
    m/=10;
  }
  if(m%2==0){
    printf("5\n");
  } else {
    n=n%10;
    while(m%5==0){
      n=(n*2)%10;
      m/=5;
    }
    printf("%lld\n",n);
  }
  return;
}

int main(void){
  run();
  return 0;
}