#include <stdio.h>
#include <stdlib.h>

int main(int c, char **v)
{
   int i, j, m, n, *s;

   /* default size: 5 */
   if (c < 2 || ((m = atoi(v[1]))) <= 0) m = 5;

   /* alloc array*/
   s = malloc(sizeof(int) * m * m);

   for (i = n = 0; i < m * 2; i++)
      for (j = (i < m) ? 0 : i-m+1; j <= i && j < m; j++)
         s[(i&1)? j*(m-1)+i : (i-j)*m+j ] = n++;

   for (i = 0; i < m * m; putchar((++i % m) ? ' ':'\n'))
      printf("%3d", s[i]);

   /* free(s) */
   return 0;
}