#include <iostream>
#include <queue>
#include <map>
#include <list>
#include <vector>
#include <string>
#include <stack>
#include <limits>
#include <climits>
#include <cassert>
#include <fstream>
#include <cstring>
#include <cmath>
#include <bitset>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <cstdio>
#include <ciso646>
#include <set>
#include <array>

using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

#define inf 0x3f3f3f3f
#define PB push_back
#define MP make_pair
#define ALL(a) (a).begin(),(a).end()
#define SET(a,c) memset(a,c,sizeof a)
#define CLR(a) memset(a,0,sizeof a)
#define pii pair<int,int>
#define pcc pair<char,char>
#define pic pair<int,char>
#define pci pair<char,int>
#define VS vector<string>
#define VI vector<int>
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define MIN(a,b) (a>b?b:a)
#define MAX(a,b) (a>b?a:b)
#define pi 2*acos(0.0)
#define INFILE() freopen("in0.txt","r",stdin)
#define OUTFILE()freopen("out0.txt","w",stdout)
#define ll long long
#define ull unsigned long long
#define eps 1e-14
#define FST first
#define SEC second
#define SETUP cin.tie(0), ios::sync_with_stdio(false), cout << setprecision(15)

namespace {
	struct input_returnner {
		int N; input_returnner(int N_ = 0) :N(N_) {}
		template<typename T> operator vector<T>() const { vector<T> res(N); for (auto &a : res) cin >> a; return std::move(res); }
		template<typename T> operator T() const { T res; cin >> res; return res; }
		template<typename T> T operator - (T right) { return T(input_returnner()) - right; }
		template<typename T> T operator + (T right) { return T(input_returnner()) + right; }
		template<typename T> T operator * (T right) { return T(input_returnner()) * right; }
		template<typename T> T operator / (T right) { return T(input_returnner()) / right; }
		template<typename T> T operator << (T right) { return T(input_returnner()) << right; }
		template<typename T> T operator >> (T right) { return T(input_returnner()) >> right; }
	};
	template<typename T> input_returnner in() { return in<T>(); }
	input_returnner in() { return input_returnner(); }
	input_returnner in(int N) { return std::move(input_returnner(N)); }
}

void solve();
/// ---template---
signed main(void) {
	SETUP;
	solve();
	return 0;
}

const ull MOD = 1e9 + 7;

string c[301];
int H, W;

int getCost(int col) {
	int x = col;
	int y = col + 1;
	int cost[301][301] = {};
	REP(d, H) {
		cost[H][d] = 0;
		cost[d][H] = 0;
		RFOR(i, 0, H - d) {
			int j = i + d;
			cost[i][j] = cost[i+1][j+1] + (c[H-i-1][x] == c[H-j-1][y]);
			if(d != 0) cost[j][i] = cost[j+1][i+1] + (c[H-j-1][x] == c[H-i-1][y]);
		}
	}
	int dp[301][301];
	dp[0][0] = 0;

	FOR(d, 1, 2*H+1) {
		FOR(i,0,d+1){
			int j = d - i;
			int a, b; a = b = inf;
			if (i > H or j > H) continue;
			if (i - 1 >= 0) a = dp[i - 1][j] + cost[i - 1][j];
			if (j - 1 >= 0) b = dp[i][j - 1] + cost[i][j - 1];
			dp[i][j] = min(a,b);
		}
	}

	return dp[H][H];
}

void solve() {
	cin >> H >> W;
	REP(i, H) cin >> c[i];
	ll res = 0;
	REP(i, W-1) {
		res += getCost(i);
	}
	cout << res << endl;
}

Measured memory_bytes: 1024