#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main() {
  int p,t;
  cin >> p >> t;
  string abbr[t];
  bitset<26> team[t];
  for (int i = 0; i < t; i++) {
    team[i].reset();
    cin >> abbr[i];
    for (char c:abbr[i]) {
      team[i].set(c-'A');
    }
  }

  // Brute force: try all possible subsets of the t teams:
  int max = pow(2,t);
  int best = 0;
  bitset<26> univ(pow(2,p)-1);

  for (int i = 1; i < max; i++) {
    bitset<26> u = univ;
    bitset<26> subset(i);
    // I don't know how to iterate over just the set bits in a bitset, so
    // convert to a string and iterate over '1's in the string:
    string s = subset.to_string();
    reverse(s.begin(),s.end()); // so bits are in same orientation as bitset
    int temp = subset.count();
    if (temp <= best) continue; // only check bigger subsets than best so far
    bool success = true;
    for (int j = s.find_first_of("1"); j != s.npos; j = s.find_first_of("1",j+1)) {
      // see if any duplicate letters:
      if (team[j].count() < abbr[j].length()) {
        success = false;
        break;
      }
      if ((u & team[j]) == team[j]) {
        u ^= team[j];
      } else {
        success = false;
        break;
      }
    }
    if (success) {
      best = temp;
    }
  }
  cout << best << endl;
}