def produce(x, y):
    K = len(x)
    left, right = 0, K-1
    while x[left] == y[left]:
        left += 1
    while x[right] == y[right]:
        right -= 1
    temp1 = x[:left] + [y[left]] + x[left:]
    temp2 = x[:right+1] + [y[right]]+ x[right+1:]
    return [temp1, temp2]
    
def match(x, y):
    now = 0
    temp = y + ["$"]
    for xx in x:
        if temp[now] == xx:
            now += 1
    return now == len(temp) - 1


N, M = map(int, input().split())
S = []
for i in range(N):
    S.append(list(input()))

kouho = produce(S[0], S[1])
ans = [1, 1]
for i in range(1, N):
    for j in range(2):
        ans[j] &= match(kouho[j], S[i])

print(sum(ans))