#include <stdio.h>
int main(void){
  char a[6],b[6];
  int i,c;
  c = 0;
  scanf("%s",&a);
  scanf("%s",&b);
  for(i = 1;i >= 6;){
    if(a[i] != 1 | a[i] != 2 | a[i] != 3 | a[i] != 4 | a[i] != 5 | a[i] != 6 | a[i] != 7 | 
       a[i] != 8 | a[i] != 9){
      c = 1;
      break;
    }else if(b[i] != 1 | b[i] != 2 | b[i] != 3 | b[i] != 4 | b[i] != 5 | b[i] != 6 | b[i] != 7 | 
       b[i] != 8 | b[i] != 9){
      c = 1;
      break;
    }else{
      i++;
    }
  }
  if(c == 1){
    printf("NG");
  }else{
    printf("OK");
  }
  return 0;
}