#include <iostream>
#include <vector>
#include <queue>
#include <deque>
using namespace std;
int main() {
int H, W;
std::cin >> H >> W;
std::vector<std::vector<bool>> v(H, std::vector<bool>(W));
v[0][0] = true;
std::vector<std::vector<char>> g(H, std::vector<char>(W));
std::vector<std::vector<int>> path(H, std::vector<int>(W));
path[0][0] = 1;
for (int i = 0; i < H; ++i) {
for (int j = 0; j < W; ++j) {
std::cin >> g[i][j];
}
}
std::deque<std::pair<int, int>> deq;
deq.push_front({0, 0});
int ans = 0;
while(!deq.empty()) {
std::pair<int, int> cur_node = deq.front();
deq.pop_front();
ans = std::max(ans, path[cur_node.first][cur_node.second]);
auto func = [&](std::pair<int, int> visit_node) {
if (visit_node.first >= 0 && visit_node.first < H &&
visit_node.second >= 0 && visit_node.second < W &&
g[visit_node.first][visit_node.second] != '.' &&
!v[visit_node.first][visit_node.second])
{
v[visit_node.first][visit_node.second] = true;
if (g[visit_node.first][visit_node.second] == g[cur_node.first][cur_node.second])
{
deq.push_front({visit_node.first, visit_node.second});
path[visit_node.first][visit_node.second] = path[cur_node.first][cur_node.second];
} else {
deq.push_back({visit_node.first, visit_node.second});
path[visit_node.first][visit_node.second] = path[cur_node.first][cur_node.second] + 1;
}
}
};
func({cur_node.first - 1, cur_node.second});
func({cur_node.first + 1, cur_node.second});
func({cur_node.first, cur_node.second + 1});
func({cur_node.first, cur_node.second - 1});
}
std::cout << ans << "\n";
return 0;
}
