#include <iostream>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>

#define MAXN 100005
#define MAXS 26
#define ll long long

using namespace std;

int n, k, d[MAXS]; 
bool a[MAXN][MAXS][MAXS], ans[MAXS][MAXS];

vector<set<int> > inAdj(26, set<int>());
vector<set<int> > outAdj(26, set<int>());

void solve() {
    cin >> n >> k;
    string s;
    int x, y;
    for (int i = 0; i < n; ++i) {
        cin >> s;
        for (int j = 0; j < s.size() - 1; ++j) {
            for (int k = j + 1; k < s.size(); ++k) {
                x = s[j] - 'A';
                y = s[k] - 'A';
                a[i][x][y] = 1;
            }
        }
    }

    for (int j = 0; j < MAXS; ++j) {
        for (int k = 0; k < MAXS; ++k) {
            ans[j][k] =1;
        }
    }

    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < MAXS; ++j) {
            for (int k = 0; k < MAXS; ++k) {
                ans[j][k] &= a[i][j][k];
            }
        }
    }

    // printf("chept1: ------\n");
    for (int j = 0; j < MAXS; ++j) {
        for (int k = 0; k < MAXS; ++k) {
            // printf("%d %d\n", j, k);
            if (ans[j][k]) {
                inAdj[k].insert(j);
                outAdj[j].insert(k);
            }
        }
    }
    // printf("chept2: ------\n");

    queue<int> q;
    for (int i = 0; i < MAXS; ++i) {
        if (inAdj[i].size() == 0) {
            q.push(i);
            d[i] = 1;
        }
    }

    int u, v;
    while (!q.empty()) {
        u = q.front(); q.pop();
        for (int v: outAdj[u]) {
            d[v] = max(d[v], d[u] + 1);
            inAdj[v].erase(u);
            if (inAdj[v].size() == 0) q.push(v);
        }
    }
    
    int ret = 1;
    for (int i = 0; i < MAXS; ++i) {
        ret = max(ret, d[i]);
    }

    cout << ret << endl;
}

int main() {

    int _ = 1;
    //cin >> _;
    while(_--) {
        solve();
    }
    return 0;
}