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

int main() {
	cin.tie(0)->ios_base::sync_with_stdio(0);

	int n, k; cin >> n >> k;
	vector<int> next(k, (1<<k)-1);

	while (n--) {
		int state = (1<<k)-1;
		for (int i = 0; i < k; i++) {
			char c; cin >> c;
			state ^= (1<<(c-'A'));
			next[c-'A'] &= state;
		}
	}

	priority_queue<pair<int,int>> pq; // cnt, state
	pq.emplace(k, (1<<k)-1);

	map<int,int> ans;
	while (pq.size()) {
		auto [_,state] = pq.top(); pq.pop();
		for (int i = 0; i < k; i++) {
			if (state & (1 << i)) {
				int nstate = state ^ (1 << i);
				nstate &= next[i];
				ans[nstate] = max(ans[nstate], ans[state]+1);
				if (nstate) {
					pq.emplace(__builtin_popcount(nstate), nstate);
				}
			}
		}
	}

	cout << ans[0] << '\n';
}