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

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL<<(n))
// functions
template <typename T> void unique(T& c){c.erase(std::unique(c.begin(), c.end()), c.end());}
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << "(" << p.first << ", " << p.second << ")"; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(nullptr); cout << fixed << setprecision(20);}
} fast_io_;

string s[330];
ll dp[330][330];
const int B = 303;
ll cntl[330][630], cntr[330][630];

int main(int argc, char const* argv[])
{
  int h, w; cin >> h >> w;
  rep(i, h)cin >> s[i];
  ll res = 0;
  for(int i = 0; i < w - 1; i++){
    rep(j, h + 1){
      rep(k, 2 * h){
        cntl[j][k] = cntr[j][k] = 0;
      }
    }
    for(int j = 0; j < h; j++){
      for(int k = 0; k < h; k++){
        if(j + k >= h)continue;
        if(s[j+k][i] == s[k][i+1])cntl[j][j+k]++;
      }
      for(int k = 1; k < 2 * h; k++)cntl[j][k] += cntl[j][k-1];
    }
    for(int j = 0; j < h; j++){
      for(int k = 0; k < h; k++){
        if(j + k >= h)continue;
        if(s[j+k][i+1] == s[k][i])cntr[j][j+k]++;
      }
      for(int k = 1; k < 2 * h; k++)cntr[j][k] += cntr[j][k-1];
    }
    rep(j, h + 1){
      rep(k, h + 1){
        dp[j][k] = inf;
      }
    }
    rep(j, h + 1){
      dp[h][j] = dp[j][h] = 0;
    }
    for(int j = h - 1; j >= 0; j--){
      for(int k = h - 1; k >= 0; k--){
        ll sc = (j <= k ? cntl[k-j][h-j-1]: cntr[j-k][h-k-1]);
        dp[j][k] = min(dp[j+1][k], dp[j][k+1]) + sc;
      }
    }
    /*
    for(int j = 0; j <= h; j++){
      for(int k = 0; k <= h; k++){
        cerr << j << " " << k << " " << dp[j][k] << endl;
      }
    }
    */

    res += dp[0][0];
  }

  cout << res << endl;
  return 0;
}


Measured memory_bytes: 4352