#include 
#include 
 
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;
}