#include <bits/stdc++.h>
using namespace std;
using int32 = int32_t;
using int64 = int64_t;
const int32 INF = 1'000'000'000;
const vector<int32> DX = {-1, +1, 0, 0};
const vector<int32> DY = {0, 0, -1, +1};
int32 N, M;
inline bool inGrid(int32 x, int32 y)
{
return (0 <= x && x < N && 0 <= y && y < M);
}
int32 main()
{
cin >> N >> M;
vector<string> grid(N);
for (auto &row : grid)
{
cin >> row;
}
deque<pair<int32, int32>> cells;
vector<vector<int32>> depth(N, vector<int32>(M, INF));
depth[0][0] = 1;
cells.emplace_back(0, 0);
int32 result = 0;
while (!cells.empty())
{
auto [x, y] = cells.front();
cells.pop_front();
result = max(result, depth[x][y]);
for (int32 d = 0; d < 4; ++d)
{
int32 nx = x + DX[d];
int32 ny = y + DY[d];
if (inGrid(nx, ny) && grid[nx][ny] != '.' && depth[nx][ny] == INF)
{
if (grid[nx][ny] == grid[x][y])
{
depth[nx][ny] = depth[x][y];
cells.emplace_front(nx, ny);
}
else
{
depth[nx][ny] = depth[x][y] + 1;
cells.emplace_back(nx, ny);
}
}
}
}
cout << result << "\n";
return 0;
}
