#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  constexpr int C = 26;
  int n, m; cin >> n >> m;
  vector<string> s(n); REP(i, n) cin >> s[i];
  if (n == 2) {
    while (s[0].back() == s[1].back()) {
      s[0].pop_back();
      s[1].pop_back();
    }
    REP(i, 2) reverse(ALL(s[i]));
    while (s[0].back() == s[1].back()) {
      s[0].pop_back();
      s[1].pop_back();
    }
    if (s[0].length() == 1) {
      cout << 2 << '\n';
      return 0;
    }
    if (s[0][1] != s[1][0]) swap(s[0], s[1]);
    if (s[0][1] != s[1][0]) {
      cout << 0 << '\n';
      return 0;
    }
    if (s[0].length() == 2) {
      cout << (s[0][0] == s[1][1] ? 2 : 1) << '\n';
    } else {
      FOR(i, 1, s[0].length()) {
        if (s[0][i] != s[1][i - 1]) {
          cout << 0 << '\n';
          return 0;
        }
      }
      assert(false);
      cout << 1 << '\n';
    }
  } else {
    REP(i, n) reverse(ALL(s[i]));
    vector<int> num[C]{};
    REP(i, n) num[s[i].back() - 'a'].emplace_back(i);
    REP(_, m + 1) {
      int c = -1;
      REP(i, C) {
        if (num[i].size() >= 2) {
          if (c != -1) {
            cout << 0 << '\n';
            return 0;
          }
          c = i;
        }
      }
      if (c == -1) {
        cout << 0 << '\n';
        return 0;
      }
      const vector<int> v = num[c];
      num[c].clear();
      for (int i : v) {
        s[i].pop_back();
        if (!s[i].empty()) num[s[i].back() - 'a'].emplace_back(i);
      }
    }
    REP(i, C) {
      if (!num[i].empty()) {
        cout << 0 << '\n';
        return 0;
      }
    }
    cout << 1 << '\n';
  }
  return 0;
}