Locking user input and counting amount of time loop happens

Im new to this so sorry if I am a bit confusing

So this is my code, its a game based around 2 players adding 1 or 2 to the variable "counter" the one who puts the final 1 or 2 adding all the numbers up to 21 wins.

So what I would like to have help with is that I want to lock the user input to only be able to select 1 or 2, not anything else because that would break the rules of the game. Also I would like to have a way to determine who won, player 1 or player 2. Like counting the amount of times the loop happens, so I can distinguish if player 1 or 2 one.

Any help would be appreciated! Thanks!

package hemtenta; import java.util.Scanner;

public class Hemtenta {

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    int counter = 0;
    int addcounter = 0;
    int sum;
    System.out.println("Welcome to 21");
    System.out.println("The game revolves about you or your opponent getting to 21 ");
    System.out.println("You both start on the same number 0, ");
    System.out.println("adding 1 or 2 to see which one of you will put the final number adding it all up to 21 and winning.");
    System.out.println("Think smart!");

    while(counter <= 20) { System.out.println("Please choose to add 1 or 2");
    addcounter = input.nextInt();
    counter += addcounter;

    System.out.println("We are now on a total of " + (counter));
    }
    if (counter==21) { System.out.println("Congratulations x! you won");
    } 
    else { System.out.println("Something went wrong! Try again");
    }

    }

}