Problem

12 /12


Custom filling - 2. Snake

Problem

Write a program that fills a matrix of N rows and M columns with serpentine natural numbers, as shown in the example.

Input
The input string contains the numbers N and M separated by a space.

Imprint
The program should display the matrix filled in the specified way.

 
Example
# Input Output
1 4 5 1 2 3 4 5
10 9 8 7 6
11 12 13 14 15
20 19 18 17 16