Read carefully the following program:

1. import java.util.Scanner;

2. public class sum

3. {

4.   public static void main(String[] args)

5.   {

6.     Scanner input = new Scanner(System.in); 

7.     int n = input.nextInt();

8.     int sum = 0;

9.     for (int i = 1; i <= n; i++) {

10.       sum = sum + i;

11.     }

12.     System.out.println(sum);

13.   }

14. }

In Big O notation, what is the run-time of this algorithm as a function of the size of the input n?