TOANDFRO.py

while(1):
    # Nhap so luong cot
    num_col = int(raw_input())
    if num_col == 0:
        break

    # Xau dau vao
    str_input = raw_input()

    # Tinh so luong cot
    num_row = len(str_input) / num_col;

    # Chuyen xau dau vao thanh dang ma tran
    # va luu dang xau binh thuong
    string = ""
    for i in range(0, num_row):
        if i % 2 == 0:
            string += str_input[i*num_col : (i+1)*num_col]
        else:
            string += (str_input[i*num_col : (i+1)*num_col])[::-1]# dao nguoc xau

    # xau ket qua
    result = ""
    for j in range(0, num_col):
        for i in range(0, num_row):
            result += string[i*num_col + j]

    print result