import sys
from collections import defaultdict

def main():
    N, M = map(int, sys.stdin.readline().split())
    S_list = [sys.stdin.readline().strip() for _ in range(N)]
    
    count = defaultdict(int)
    
    for s in S_list:
        seen = set()
        for pos in range(M + 1):
            for c in 'abcdefghijklmnopqrstuvwxyz':
                # Generate T by inserting c at position pos
                t = s[:pos] + c + s[pos:]
                if t not in seen:
                    seen.add(t)
                    count[t] += 1
    
    result = 0
    for t, cnt in count.items():
        if cnt == N:
            result += 1
    print(result)

if __name__ == "__main__":
    main()