Zig Zag

using System;
using System.Linq;

namespace Zig_Zag
{
    class Program
    {
        static void Main()
        {
            int[] size = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int n = size[0];
            int m = size[1];
            int[,] matrix = new int[n, m];
            int initialNum = 1;
            int startRow = 0;
            int currRow = 0;
            int currCol = 0;
            ulong sumPath = 0;
            FindMatrixSumFollowingZigZagPath(n, m, matrix, initialNum, currRow, currCol, startRow, sumPath);

        }

        private static void FindMatrixSumFollowingZigZagPath(int n, int m, int[,] matrix, int initialNum, int startRow, int currRow, int currCol, ulong sumPath)
        {
            initialNum = FillMatrix(n, m, matrix, initialNum, startRow);
            for (int row = 0; row < n; row += 2)
            {
                for (int col = 0; col < m; col += 2)
                {
                    if (row == 0 || row == n - 1 || col == 0 || col == m - 1)
                    {
                        sumPath += (ulong)matrix[row, col];
                    }
                    else
                    {
                        sumPath += (ulong)(matrix[row, col] * 2);
                    }
                }
            }
            for (int row = 1; row < n; row += 2)
            {

                for (int col = 1; col < m; col += 2)
                {
                    if (col == 0 || col == m - 1)
                    {
                        sumPath += (ulong)matrix[row, col];
                    }
                    else
                    {
                        sumPath += (ulong)(matrix[row, col] * 2);
                    }

                }
            }

            Console.WriteLine(sumPath);
        }

        private static int FillMatrix(int n, int m, int[,] matrix, int initialNum, int startRow)
        {
            for (int row = 0; row < n; row++)
            {
                for (int col = 0; col < m; col++)
                {
                    matrix[row, col] = initialNum;
                    initialNum += 3;
                }
                initialNum = matrix[row, startRow + 1];
            }

            return initialNum;
        }
    }
}