#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
#include <queue>
using namespace std;
vector<int> radd = { -1, 0, 1, 0 };
vector<int> cadd = { -1, 0, 1, 0 };
int main()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
int h, w;
cin >> h >> w;
vector<vector<char>> trk(h + 2, vector<char>(w + 2, '.'));
for (int i = 1; i <= h; i++) for (int j = 1; j <= w; j++) cin >> trk[i][j];
priority_queue<pair<int, pair<int, int>>> bfs;
int ans = 0;
vector<vector<int>> dist(h + 2, vector<int>(w + 2, 0));
bfs.push({ -1, {1, 1} });
while (!bfs.empty())
{
int nans = -bfs.top().first;
int r = bfs.top().second.first;
int c = bfs.top().second.second;
bfs.pop();
if (dist[r][c] == 0)
{
ans = nans;
dist[r][c] = nans;
for (int dir = 0; dir < 4; dir++)
{
if (trk[r + radd[dir]][c + cadd[dir]] == trk[r][c]) bfs.push({ -nans, {r + radd[dir], c + cadd[dir]} });
else if (trk[r + radd[dir]][c + cadd[dir]] != '.') bfs.push({ -nans - 1, {r + radd[dir], c + cadd[dir]} });
}
}
}
cout << ans;
}
