import sys
from collections import defaultdict

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

    if N == 0:
        print(0)
        return

    # Function to generate all possible T's by inserting one character into s
    def generate_T(s):
        possible = set()
        for i in range(len(s)+1):
            for c in 'abcdefghijklmnopqrstuvwxyz':
                new_s = s[:i] + c + s[i:]
                possible.add(new_s)
        return possible

    # Generate all possible T's for each S_i
    T_sets = []
    for s in S:
        T_set = generate_T(s)
        T_sets.append(T_set)
        # Early exit if any T_set is empty
        if not T_set:
            print(0)
            return

    # Compute intersection of all T_sets
    common = T_sets[0]
    for t_set in T_sets[1:]:
        common.intersection_update(t_set)
        if not common:
            print(0)
            return

    print(len(common))

if __name__ == "__main__":
    main()