import java.util.*; 
import java.io.*;

class Main {
   public static String CodelandUsernameValidation(String str) {
    // code goes here 

    if(str.length() < 4 || str.length() > 25 || Character.isLetter(str.charAt(0)) == false || str.charAt(str.length()-1) == '_') {
      return "false";
    } 
    else{
      for(int i=0;i<str.length();i++){
        if(Character.isLetter(str.charAt(i)) || Character.isDigit(str.charAt(i)) || str.charAt(i) == '_'){
          continue;
        }
        else{
          return "false";
        }
      }
    }
    return "true";
    
  }

  public static void main (String[] args) {  
    // keep this function call here     
    Scanner s = new Scanner(System.in);
    System.out.print(CodelandUsernameValidation(s.nextLine())); 
  }

}