任何人请帮我打破while循环，我只想结束程序时，用户键入什么，但为什么不能工作？请帮忙，谢谢。

import java.util.Random;
import java.util.Scanner;
import java.lang.Math;

public class Determining_Pi_Experiment {
    public static void main(String[] args) {
        while (true) {
            System.out.println("Press 'enter' to exit, or type an integer number indicating for how many times you " +
                    "want the experiment run: ");
            Scanner input = new Scanner(System.in);
            if(!input.equals(null)) {
                if(input.hasNextInt()) {

                    System.out.println("Processing...");
                    Random rand = new Random();
                    int ExperimentTimes = input.nextInt();
                    double count_success = 0;
                    double Pi = 0;

                    for (int i = 0; i < ExperimentTimes; ++i) {

                        double x = rand.nextDouble();
                        double y = rand.nextDouble();

                        double distance = Math.pow(Math.pow((x - 0.5), 2) + Math.pow((y - 0.5), 2), 0.5);

                        if (distance <= 0.5) {
                            ++count_success;
                        }
                    }
                    Pi = (count_success / ExperimentTimes) * 4;
                    System.out.println("Pi is approximately equal to: " + Pi);
                }
                else {
                    System.out.println("Invalid input.");
                }
            }
            else if(input.equals(null)) {
                System.exit(0);
            }
        }
    }
}