#!/usr/bin/env python3
import sys

sys.setrecursionlimit(100000)
n, l = map(int, input().split())
names, trie = [input() for _ in range(n)], dict()
for name in names:
    curr = trie
    for i, c in enumerate(name):
        if c not in curr:
            curr[c] = name[i + 1:]
            break
        if type(curr[c]) == str:
            curr[c] = {curr[c][0]: curr[c][1:]}
        curr = curr[c]


def size(t):  # -> (total number of characters required to store, number of strings covered in this sub-trie)
    if type(t) == str: return 0, 1
    return tuple(sum(l) for l in zip(*((b + a, b) for a, b in (size(s) for s in t.values()))))


print(size(trie)[0])