using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

    public static int[] FindDiagonalOrder(int[][] matrix) {

        if(matrix.Length == 0) 

            return new int[0];

        int i = 0, dir = 1, r = 0, c = 0, m = matrix.Length, n = matrix[0].Length;

        int[] ans = new int[m * n];

        while(i < m * n) {

            if (dir == 1) {  // upright

                ans[i++] = matrix[r][c];

                while (r - 1 >= 0 && c + 1 < n) 

                {

                    ans[i++] = matrix[--r][++c];

                }

                if (c+1 < n) 

                    c++;

                else if (r + 1 < m) 

                    r++;

                dir = 0;

            } else {  // downleft

                ans[i++] = matrix[r][c];

                while (r + 1 < m && c - 1 >= 0) 

                {

                    ans[i++] = matrix[++r][--c];

                }

                if (r + 1 < m) 

                    r++;

                else if (c + 1 < n) 

                    c++;

                dir = 1;

            }

        }

        return ans;

    }

}