#!/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)]
ans = 0
for i in range(26):
    for j in range(m+1):
        tmp = []
        for k in range(j):
            tmp.append(s[0][k])
        tmp.append(chr(i+ord('a')))
        for k in range(j,m):
            tmp.append(s[0][k])
        for ii in range(1,n):
            now = 0
            for k in range(m+1):
                if now < m and tmp[k] == s[ii][now]:
                    now += 1
            if now != m:
                break
        else:
            ans += 1
print(ans)