class Solution {
public static boolean solution(String s) {
boolean answer = true;
if(s.length()!=4 && s.length()!=6) return false;
for(int i=0; i<s.length(); i++){
String str = "";
str += s.charAt(i);
if (!"0123456789".contains(str)) {
return false;
}
}
return answer;
}
}