using System;

public class Program

{

    public static void Main()

    {

        //1.

        int i;

        long result = 0;

        for (i=1777;i<=2022;i++) 

        {

            result += i;

        }

        Console.WriteLine("Sum of the numbers between 1777 and 2022 : " + result);

        // Gauss's Method

        int m = 1777 - 1;

        int n = 2022;

        double ans = (0.5*n)*(n+1) - (0.5*m)*(m+1);

        Console.WriteLine("Sum of the numbers between 1777 and 2022 : " + ans);

​

        // product of first 10 integer numbers

        // while loop

        int j = 1;

        int res = 1;

        while (j<=10)

        {

            res *= j;

            j++;

        }

        Console.WriteLine("Product of first 10 integer numbers is: " + res);

        // for loop

        res = 1;

        for (j=1;j<=10;j++)

        {

            res *= j;

        }

        Console.WriteLine("Product of first 10 integer numbers is: " + res);

        // product of first 20 integer numbers

        // while loop

        j = 1;

        long r = 1;

        while (j<=20)

        {

            r *= j;

            j++;

        }

        Console.WriteLine("Product of first 20 integer numbers is: " + r);

        // for loop

        r = 1;

        for (j=1;j<=20;j++)

        {

            r *= j;

        }

        Console.WriteLine("Product of first 20 integer numbers is: " + r);

    }

}