#include <iostream>
#include <vector>
#include <queue>
using namespace std;
int H, W;
vector<vector<char>> grid;
int rD[] = {0,1,0,-1};
int cD[] = {1,0,-1,0};
int BFS(int startR, int startC) {
deque<pair<int, int>> q;
q.push_front({ startR, startC });
vector<vector<int>> sol(H, vector<int>(W, 0));
sol[startR][startC] = 1;
int ans = 1;
while (!q.empty()) {
auto [curR, curC] = q.front(); q.pop_front();
ans = max(ans, sol[curR][curC]);
for (int i = 0; i < 4; ++i) {
int nR = curR + rD[i];
int nC = curC + cD[i];
if (nR < 0 || nR >= H || nC < 0 || nC >= W || grid[nR][nC] == '.' || sol[nR][nC] != 0) continue;
if (grid[curR][curC] == grid[nR][nC]) {
sol[nR][nC] = sol[curR][curC];
q.push_front({ nR,nC });
}
else {
sol[nR][nC] = sol[curR][curC] + 1;
q.push_back({ nR,nC });
}
}
}
return ans;
}
int main()
{
cin >> H >> W;
grid.assign(H, vector<char>(W));
for (int i = 0; i < H; ++i) {
for (int j = 0; j < W; ++j) {
cin >> grid[i][j];
}
}
cout << BFS(0, 0);
}
