Let's assume that we are given a matrix *b* of size *x* × *y*, let's determine the operation of mirroring matrix *b*. The mirroring of matrix *b* is a 2*x* × *y* matrix *c* which has the following properties:
 -  the upper half of matrix *c* (rows with numbers from 1 to *x*) exactly matches *b*; -  the lower half of matrix *c* (rows with numbers from *x* + 1 to 2*x*) is symmetric to the upper one; the symmetry line is the line that separates two halves (the line that goes in the middle, between rows *x* and *x* + 1). 
Sereja has an *n* × *m* matrix *a*. He wants to find such matrix *b*, that it can be transformed into matrix *a*, if we'll perform on it several (possibly zero) mirrorings. What minimum number of rows can such matrix contain?
The first line contains two integers, *n* and *m* (1 ≤ *n*, *m* ≤ 100). Each of the next *n* lines contains *m* integers — the elements of matrix *a*. The *i*-th line contains integers *a*<sub class="lower-index">*i*1</sub>, *a*<sub class="lower-index">*i*2</sub>, ..., *a*<sub class="lower-index">*im*</sub> (0 ≤ *a*<sub class="lower-index">*ij*</sub> ≤ 1) — the *i*-th row of the matrix *a*.
# @Author: Justin Hershberger
# @Date:   21-03-2017
# @Filename: 426B.py
# @Last modified by:   Justin Hershberger
# @Last modified time: 21-03-2017

#Justin Hershberger
#Py3.5

import fileinput

def check_matrix(m):
    first_half = []
    second_half = []
    for i in range(len(m) // 2):
        first_half.append(m[i])
    for j in range(len(m), len(m) // 2, -1):
        second_half.append(m[j-1])

    if (first_half == second_half):
        return first_half
    else:
        return -1;


if __name__ == '__main__':
    n,m = map(int, input().split())

    matrix = []
    for arg in range(n):
        matrix.append(input().split())

    if len(matrix) % 2 == 0:
        result = matrix
        num_rows = 0
        while(result != -1):
            result = check_matrix(result)
            if result != -1:
                num_rows = len(result)
        print(num_rows)
    else:
        print(n)
    # print(matrix)
