def is_subsequence(s, t):
    it = iter(t)
    return all(c in it for c in s)

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
    
    # Generate all possible T from S[0]
    s0 = S[0]
    candidates = set()
    for pos in range(M + 1):
        for c in 'abcdefghijklmnopqrstuvwxyz':
            new_t = s0[:pos] + c + s0[pos:]
            candidates.add(new_t)
    
    count = 0
    for t in candidates:
        valid = True
        for s in S[1:]:
            if not is_subsequence(s, t):
                valid = False
                break
        if valid:
            count += 1
    print(count)

if __name__ == "__main__":
    main()