#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>
#include <fstream>
#include <bitset>
   
using namespace std;
   
 
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
#define rforeach(it, c) for (__typeof__((c).rbegin()) it=(c).rbegin(); it != (c).rend(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define CL(arr, val) memset(arr, val, sizeof(arr))
#define COPY(dest, src) memcpy(dest, src, sizeof(dest))
#define ten(n) ((long long)(1e##n))
#define bin(n) (1LL << (n))
#define erep(i, n) for (int i = 0; i <= (int)(n); ++i)
#define revrep(i, n) for (int i = (n); i >= 0; --i)
#define pb push_back

template <class T> void chmax(T& a, const T& b) { a = max(a, b); }
template <class T> void chmin(T& a, const T& b) { a = min(a, b); }

template <class T> void uniq(T& c) { sort(c.begin(), c.end()); c.erase(unique(c.begin(), c.end()), c.end()); }
 
template <class T> string to_s(const T& a) { ostringstream os; os << a; return os.str(); }
template <class T> T to_T(const string& s) { istringstream is(s); T res; is >> res; return res; }

template <typename T> void print_container(ostream& os, const T& c) { const char* _s = " "; if (!c.empty()) { __typeof__(c.begin()) last = --c.end(); foreach (it, c) { os << *it; if (it != last) cout << _s; } } }
template <typename T> ostream& operator<<(ostream& os, const vector<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const set<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const multiset<T>& c) { print_container(os, c); return os; }
template <typename T> ostream& operator<<(ostream& os, const deque<T>& c) { print_container(os, c); return os; }
template <typename T, typename U> ostream& operator<<(ostream& os, const map<T, U>& c) { print_container(os, c); return os; }
template <typename T, typename U> ostream& operator<<(ostream& os, const pair<T, U>& p) { os << "(" << p.first << ", " << p.second << ")"; return os; }

template <class T> void print(T a, int n, const string& deli = " ", int br = 1) { for (int i = 0; i < n; ++i) { cout << a[i]; if (i + 1 != n) cout << deli; } while (br--) cout << endl; }
template <class T> void print2d(T a, int w, int h, int width = -1, int br = 1) { for (int i = 0; i < h; ++i) { for (int j = 0; j < w; ++j) {    if (width != -1) cout.width(width); cout << a[i][j] << ' '; } cout << endl; } while (br--) cout << endl; }

template <class T> void input(T& a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }
template <class T> void input(T* a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }

void fix_pre(int n) { cout.setf(ios::fixed, ios::floatfield); cout.precision(10); }
void fast_io() { cin.tie(0); ios::sync_with_stdio(false); }
#define trace(x) (cout << #x << ": " << (x) << endl)
 
bool in_rect(int x, int y, int w, int h) { return 0 <= x && x < w && 0 <= y && y < h; }

typedef long long ll;
typedef pair<int, int> pint;

// y(v): v>^<  y(^): ^>v<
const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { 1, 0, -1, 0 };

const double PI = acos(-1.0);
#define mp make_pair



int main()
{
    int h, w;
    cin >> h >> w;
    string s[200];
    input(s, h);

    int bits[bin(16)];
    rep(mask, bin(w))
        bits[mask] = __builtin_popcount(mask);

    
    const int inf = ten(6);
    int cur[bin(16)], next[bin(16)];
    fill_n(cur, bin(w), -inf);
    rep(mask, bin(w))
        if (bits[mask] == s[0].size())
            cur[mask] = 0;
    
    rep(y, h)
    {
        // hor
        rep(mask, bin(w))
        {
            if (bits[mask] == s[y].size())
            {
                int pos[16];
                int k = 0;
                rep(x, w)
                    if (mask >> x & 1)
                        pos[k++] = x;
                rep(i, s[y].size() - 1)
                    if (s[y][i] == s[y][i + 1] && pos[i] + 1 == pos[i + 1])
                        ++cur[mask];
            }
            else
                cur[mask] = -inf;
        }

        if (y == h - 1)
            break;

        // ver
        rep(x, w)
        {
            fill_n(next, bin(w), -inf);
            // mask: [next_mask(x bits) + cur_mask(w - x bits)]
            rep(mask, bin(w))
            {
                int cur_mask = mask & ((bin(w - x) - 1) << x);
                int next_mask = mask & (bin(x) - 1);
                int cur_i = (int)s[y].size() - bits[cur_mask];
                int next_i = bits[next_mask];
                if (cur[mask] < 0 || cur_i < 0)
                    continue;


                // empty
                chmax(next[mask & ~bin(x)], cur[mask]);

                // put s[y + 1][next_i]
                if (next_i < s[y + 1].size())
                {
                    int adjacent = (mask >> x & 1) && cur_i < s[y].size() && s[y][cur_i] == s[y + 1][next_i];
                    chmax(next[mask | bin(x)], cur[mask] + adjacent);
                }
            }
            swap(cur, next);
        }
    }

    int res = 2 * *max_element(cur, cur + bin(w));
    cout << res << endl;
}

Measured memory_bytes: 1984