// https://oj.uz/problem/view/BOI13_tracks
#include <bits/stdc++.h>
using namespace std;
#define DEBUG 0
#if DEBUG
#define HAS_EXTRA 1
#include "./codeforces/debug.hpp"
#endif
typedef long long int ll;
typedef vector<int> vint;
typedef vector<ll> vlong;
#define loop(a, b) for (int i = a; i < b; i++)
#define loop0(a) for (int i = 0; i < a; i++)
#define all(x) x.begin(), x.end()
#define contains(v, x) (find(begin(v), end(v), x) != end(v))
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v)
{
for (int i = 0; i < v.size(); ++i)
{
os << v[i];
if (i != v.size() - 1)
os << " ";
}
return os;
}
inline void printV(const vector<pair<int, int>> &v)
{
for (auto &[x, y] : v)
cout << '(' << x << ',' << y << ") ";
cout << '\n';
}
vector<vector<char>> readGrid()
{
int n, m;
cin >> n >> m;
vector<vector<char>> res(n, vector<char>(m, 'a'));
loop0(n) for (int j = 0; j < m; j++)
cin >>
res[i][j];
return res;
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
vector<vector<char>> g = readGrid();
vector<vint> moves = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
int c = 0;
vector<pair<int, int>> pos = {make_pair(0, 0)};
while (!pos.empty())
{
// printV(pos);
vector<pair<int, int>> p(pos.begin(), pos.end());
vector<pair<int, int>> newpos;
pos.clear();
char curr = g[p[0].first][p[0].second];
// cout << curr << endl;
// BFS from p
while (!p.empty())
{
vector<pair<int, int>> np;
for (auto pr : p)
{
loop0(4)
{
int x = pr.first + moves[i][0];
int y = pr.second + moves[i][1];
if (x < 0 || x >= g.size() || y < 0 || y >= g[0].size())
continue;
char val = g[x][y];
if (val != curr && val != '.')
{
g[pr.first][pr.second] = '.';
newpos.push_back(make_pair(x, y));
}
if (val == curr)
{
g[pr.first][pr.second] = '.';
np.push_back(make_pair(x, y));
}
}
}
p.swap(np);
}
pos.swap(newpos);
c++;
}
cout << c;
return 0;
}
