//0 1 1 0 1
//0 1 0 0 1
//1 0 0 1 1
//0 1 1 0 1
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast,unroll-loops")
// #pragma GCC target("avx2")
using namespace std;
#define F first
#define S second
#define pb push_back
#define sze size()
#define all(x) x.begin() , x.end()
#define wall__ cout << "--------------------------------------\n";
#define kids int mid = (tl + tr) >> 1, cl = v << 1, cr = v << 1 | 1
#define file_io freopen("input.cpp", "r", stdin); freopen("output.cpp", "w", stdout);
typedef long long ll;
typedef long double dl;
typedef pair < short int , short int > pii;
typedef pair < int , ll > pil;
typedef pair < ll , int > pli;
typedef pair < ll , ll > pll;
typedef pair < int , pii > piii;
typedef pair < ll, pll > plll;
const ll N = 4000 + 3;
const ll M = N * N;
const ll mod = 1e9 + 7;
const ll inf = 2e16;
const ll rinf = -2e16;
const ll INF = 1e9 + 10;
const ll rINF = -1e9 - 10;
const ll lg = 32;
int n, m, h[N][N], ans;
char c[N][N];
int main() {
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for (int i = 1; i <= n; i++) c[i][0] = '.';
for (int i = 1; i <= m; i++) c[0][i] = '.';
for (int i = 1; i <= n; i++)
for (int j = 1; j <= m; j++) {
cin >> c[i][j];
h[i][j] = INF;
}
deque < pii > q; q.pb({1, 1}); h[1][1] = 0;
while (q.sze) {
pii v = q.back();
q.pop_back();
short int x = v.F, y = v.S; ans = max(h[x][y], ans);
for (short int i = -1; i <= 1; i++) {
if (c[x + i][y] == c[x][y]) {
if (h[x][y] < h[x + i][y]) {
h[x + i][y] = h[x][y];
q.push_back({x + i, y});
}
} else if (c[x + i][y] != '.') {
if (h[x][y] + 1 < h[x + i][y]) {
h[x + i][y] = h[x][y] + 1;
q.push_front({x + i, y});
}
}
if (c[x][y + i] == c[x][y]) {
if (h[x][y] < h[x][y + i]) {
h[x][y + i] = h[x][y];
q.push_back({x, y + i});
}
} else if (c[x][y + i] != '.') {
if (h[x][y] + 1 < h[x][y + i]) {
h[x][y + i] = h[x][y] + 1;
q.push_front({x, y + i});
}
}
}
}
cout << ++ans << '\n';
return 0;
}
/*
5 12
RRRRRRRR....
F...F..RRRRR
R...F..FR..R
RR..FF.FFFFR
FRRRRFFFFFRR
*/
//shrek will AC this;
