import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class SumCalculator {
    static class Worker implements Runnable {
        private final int n;

        Worker(int n) {
            this.n = n;
        }

        @Override
        public void run() {
            int sum = calculateSum(n);
            System.out.println("Sum of first " + n + " integers: " + sum + " (Calculated by " + Thread.currentThread().getName() + ")");
        }

        private int calculateSum(int n) {
            return n * (n + 1) / 2; // Formula for sum of first n integers
        }
    }

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executor = Executors.newFixedThreadPool(4); // 4 worker threads

        // Submitting tasks with different values of 'n'
        for (int i = 1; i <= 8; i++) {
            executor.submit(new Worker(i * 10));
        }

        executor.shutdown();
        executor.awaitTermination(1, TimeUnit.MINUTES);

        System.out.println("All tasks completed.");
    }
}