def main():
    import sys
    input = sys.stdin.read().split()
    idx = 0
    N = int(input[idx])
    idx += 1
    M = int(input[idx])
    idx += 1
    S = []
    for _ in range(N):
        S.append(input[idx])
        idx += 1

    first = S[0]
    candidates = set()
    for i in range(M+1):
        for c in 'abcdefghijklmnopqrstuvwxyz':
            newT = first[:i] + c + first[i:]
            candidates.add(newT)

    count = 0
    for T in candidates:
        valid = True
        for s in S:
            if len(s) != M or len(T) != M + 1:
                valid = False
                break
            i = 0  # pointer for T
            j = 0  # pointer for s
            while i < len(T) and j < len(s):
                if T[i] == s[j]:
                    j += 1
                i += 1
            if j != len(s):
                valid = False
                break
        if valid:
            count += 1

    print(count)

if __name__ == "__main__":
    main()