#include <bits/stdc++.h>
using namespace std;
#define int long long
constexpr int inf = 1e18;
constexpr int maxn = 2e5 + 5;
constexpr int mod = 998244353;

inline vector<int> calc(string &s, string &t)
{
  int n = (int)s.size();
  vector<int> res(n + 1);
  int c = 0;
  for (int i = 0; i < n; i ++)
  {
    if (s[i] == t[c])
      c ++;
    res[i + 1] = c;
  }
  return res;
}

inline void solve()
{
  int n, m, ans = 0; cin >> n >> m;
  vector<string> s(n);
  for (auto &x : s) cin >> x;
  
  vector x(n - 1, vector<int>()), y(x);
  for (int i = 0; i < n - 1; i ++)
    x[i] = calc(s[0], s[i + 1]);
  for (auto &x : s) reverse(x.begin(), x.end());
  for (int i = 0; i < n - 1; i ++)
    y[i] = calc(s[0], s[i + 1]);
  for (auto &x : s) reverse(x.begin(), x.end());
  for (int i = 0; i <= m; i ++)
  {
    for (int j = 0; j < 26; j ++)
    {
      if (i != m && s[0][i] == 'a' + j) continue;
      int f = 1;
      for (int k = 0; k < n - 1; k ++)
        if (x[k][i] + y[k][m - i] < m - 1 || s[k + 1][x[k][i]] != 'a' + j) 
        {
          f = 0;
          break;
        }
      ans += f;
    }
  }
  cout << ans << "\n";
}

signed main()
{
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  solve();
  return 0;
}
/*
The details you should care:

*/