#!/usr/bin/env PyPy3

from collections import Counter, defaultdict, deque
import itertools
import re
import math
from functools import reduce
import operator
import bisect
import heapq
import functools
mod=10**9+7

import sys
input=sys.stdin.readline

n,m=map(int,input().split())
s=[input().rstrip() for _ in range(n)]
ansl = []
ansl2 = []
if n > 2:
    for j in range(m):
        l = [0] * 26
        for i in range(n):
            l[ord(s[i][j])-ord('a')] += 1
        if max(l) == n:
            for k in range(26):
                if l[k] == n:
                    ansl.append(chr(k+ord('a')))
        elif max(l) == n - 1:
            for k in range(26):
                if l[k] == n - 1:
                    ansl.append(chr(k+ord('a')))
                if l[k] == 1:
                    pos = k
            for ii in range(n):
                if ord(s[ii][j])-ord('a') == pos:
                    for jj in range(j,m):
                        ansl.append(s[ii][jj])
                    break
            break
        else:
            print(0)
            exit()
    for i in range(n):
        now = 0
        for aa in ansl:
            if now < m and aa == s[i][now]:
                now += 1
        if now < m:
            print(0)
            exit()
    print(1)
else:
    for j in range(m):
        l = [0] * 26
        for i in range(n):
            l[ord(s[i][j])-ord('a')] += 1
        if max(l) == n:
            for k in range(26):
                if l[k] == n:
                    ansl.append(chr(k+ord('a')))
                    ansl2.append(chr(k+ord('a')))
        else:
            ansl.append(s[1][j])
            ansl2.append(s[0][j])
            for jj in range(j,m):
                ansl.append(s[0][jj])
                ansl2.append(s[1][jj])
            break
    c = 0
    for i in range(n):
        now = 0
        for aa in ansl:
            if now < m and aa == s[i][now]:
                now += 1
        if now != m:
            break
    else:
        c += 1
    for i in range(n):
        now = 0
        for aa in ansl2:
            if now < m and aa == s[i][now]:
                now += 1
        if now != m:
            break
    else:
        c += 1
    print(c)