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 change(l,m,s0,x):
    if l == m:
        cmp = x
    elif l < m:
        cmp = s0[l]
    else:
        cmp = s0[l-1]
    return cmp
def check(s0,m,x,s):
    l = 0
    cnt = 0
    for i in range(M):
        cmp = change(l,m,s0,x)
        if cmp == s[i]:
            l += 1
        else:
            l += 1
            if cnt :
                return False
            cmp = change(l,m,s0,x)
            if cmp == s[i]:
                l += 1
                cnt += 1
            else:
                return False
    return True


def allcheck(s0,m,x):
    for i in range(1,N):
        if check(s0,m,x,S[i]):
            pass
        else:
            return False
    return True

ans = 0
for m in range(M+1):
    for x in range(26):
        if allcheck(S[0],m,x):
            ans += 1
print(ans)