(Java) If Case Void Help

[St4nley]

import java.util.Scanner; // IMPORT SCANNER

public class BasicCalculator {
    public static void main(String[] args) {
      Scanner Input =  new Scanner (System.in); //DECLARING SCANNER VARIABLE
      double firstNum, secondNum, answer;      //DECLARING VARIABLES
      double caseThird;
      System.out.println("Enter First Number: ");
      firstNum = Input.nextDouble(); //whatever i type in keyboard = firstNumber
      System.out.println("Enter Second Number: ");
      secondNum = Input.nextDouble(); //whatever i type in keyboard = secondNumber
      answer = firstNum + secondNum;
      System.out.println(answer);
     
      if (answer == 20) {
         
          System.out.println("Enter a Third Number");
          caseThird = Input.nextDouble();
          answer = firstNum + secondNum + caseThird;
          System.out.print("The Total = ");
          System.out.println(answer);
      }else{
          System.out.println("Null");

right before the if statement it says print answer, BUT i want to void that print answer IF my if statement is in run. Is there any way to do this?
Thanks!