#include <bits/stdc++.h>

using namespace std;

//#define int long long
#define ld long double
#define el '\n'
#define fi first
#define se second

#define Nine_seconds ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);

const int INF = 1e9;

bool relax(int &a, int b) {
    if (a >= b) return false;
    a = b;

    return true;
}

void run_case(int tc) {
    int n, k;
    cin >> n >> k;
    vector<string> a(n);
    vector<vector<bool>> ok(26, vector<bool>(26, true));

    for (int i = 0; i < n; i++) {
        cin >> a[i];
        for (auto &c: a[i])
            c = tolower(c);

        for (int j = k - 1; j >= 0; j--)
            for (int o = j - 1; o >= 0; o--)
                ok[a[i][j] - 'a'][a[i][o] - 'a'] = false;
    }

    vector<vector<int>> dp(k + 1, vector<int>(26, -INF));
    dp[0] = vector<int>(26, 0);
    string &s = a[0];
    for (int i = 0; i < k; i++) {
        for (int prv = 0; prv < 26; prv++) {

            relax(dp[i + 1][prv], dp[i][prv]);

            if  (ok[prv][s[i] - 'a'])
                relax(dp[i + 1][s[i] - 'a'], dp[i][prv] + 1);
        }
    }

    cout << *max_element(dp[k].begin(), dp[k].end()) << el;
}


int32_t main() {
    Nine_seconds        /*Turn Off for Interactive Problems*/

    int _t = 1;
    //cin >> _t;
    for (int i = 1; i <= _t; i++) {
        run_case(i);
    }
}