def main():
    import sys
    from collections import defaultdict

    N, M = map(int, sys.stdin.readline().split())
    S = [sys.stdin.readline().strip() for _ in range(N)]

    possible = None

    for s in S:
        candidates = defaultdict(int)
        for i in range(M + 1):
            for c in 'abcdefghijklmnopqrstuvwxyz':
                t = s[:i] + c + s[i:]
                candidates[t] += 1
        if possible is None:
            possible = candidates
        else:
            new_possible = defaultdict(int)
            for t, cnt in possible.items():
                if t in candidates:
                    new_possible[t] = cnt + 1
            possible = new_possible
            if not possible:
                break

    if possible is None:
        print(0)
    else:
        count = 0
        for t, cnt in possible.items():
            if cnt == N:
                count += 1
        print(count)

if __name__ == "__main__":
    main()