from collections import deque
N,M = map(int,input().split())
S = []
def tmp(x):
    return ord(x) -ord('a')
for _ in range(N):
    s = list(map(tmp,list(input())))
    S.append(s)
def check(s,t):
    l = 0
    cnt = 0
    for i in range(len(s)):
        if s[i] == t[l]:
            l += 1
        else:
            l += 1
            if cnt:
                return False
            if s[i] == t[l]:
                l+=1
                cnt += 1
            else:
                return False
    return True
def f(m,x,s0):
    return s0[:m] + [x] + s0[m:]

def allcheck(t):
    for i in range(N):
        if check(S[i],t):
            pass
        else:
            return False
    return True
ans = 0
for m in range(M+1):
    for x in range(26):
        t = f(m,x,S[0])
        if allcheck(t):
            ans += 1
print(ans)