Star Arrangements Solution:

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Kattis {
    private static int ball = 1;
    public static void main(String[] args) throws Exception{
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int stars = Integer.parseInt(reader.readLine());
        StringBuilder sb = new StringBuilder(stars+":\n");
        for(int firstRow = 2; firstRow <= (stars/2) +1; firstRow++){
            int remainder = stars%(2 * firstRow -1);
            if(remainder == 0 || remainder - firstRow == 0)
                sb.append(firstRow + "," + (firstRow-1) + "\n");
            remainder = stars % firstRow;
            if(remainder == 0)
                sb.append(firstRow + "," + firstRow + "\n");
        }
        System.out.print(sb);
    }
}