#include <bits/stdc++.h>
#include <unistd.h>

using namespace std;

#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}


typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),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; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0, -1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
//#define mp make_pair


int h, w;
vii c(311, vi(311));
vll dp(311, vl(311));
vll hyou(311, vl(311));

ll calc(int j, int ri, int li) {
  if (dp[ri][li] >= 0) return dp[ri][li];
  int rii = ri - 1, lii = li - 1;
  int cnt = hyou[ri][li];
  ll res = INF;
  if (ri > 0) {
    chmin(res, calc(j, ri - 1, li));
  }
  if (li > 0) {
    chmin(res, calc(j, ri, li - 1));
  }
  res += cnt;
  dp[ri][li] = res;
  return res;
}
        

int main() {
  cin >> h >> w;
  rep (i, h) {
    rep (j, w) {
      char cc;
      cin >> cc;
      c[i][j] = cc - 'a';
    }
  }
  ll ans = 0;
  rep (j, w - 1) {
    rep (i, h + 1) {
      rep (k, h + 1) {
        dp[i][k] = -1;
        hyou[i][k] = 0;
      }
    }
    dp[0][0] = 0;
    rep (diff, h + 1) {
      rep1 (li, h) {
        int ri = li + diff;
        if (ri > h) break;
        hyou[li][ri] = hyou[li - 1][ri - 1] + (int)(c[li - 1][j] == c[ri - 1][j + 1]);
        hyou[ri][li] = hyou[ri - 1][li - 1] + (int)(c[ri - 1][j] == c[li - 1][j + 1]);
      }
    }
    ll add = calc(j, h, h);
    /*
    DEBUG(add);
    rep (i, h + 1) {
      rep (k, h + 1) {
        printf("%2lld ", hyou[i][k]);
      }
      cout << endl;
    }
    //*/
    ans += add;
  }
  cout << ans << endl;
}


Measured memory_bytes: 2176