#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
using namespace std;
const int sz = 4e3 + 5;
int n, m, used[sz][sz];
char c[sz][sz];
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
for(int i = 0; i < n; i++) for(int j = 0; j < m; j++) cin >> c[i][j];
int ans = 0, cur = 0;
queue<array<int, 2>> q[2];
q[cur].push({0, 0});
used[0][0] = 1;
while(!q[cur].empty())
{
ans++;
assert(ans < n * m);
while(!q[cur].empty())
{
int x = q[cur].front()[0], y = q[cur].front()[1];
q[cur].pop();
for(int i = 0; i < 4; i++)
{
int nx = x + dx[i], ny = y + dy[i];
if(nx < 0 || n <= nx || ny < 0 || m <= ny || used[nx][ny] || c[nx][ny] == '.') continue;
if(c[nx][ny] == c[x][y]) q[cur].push({nx, ny});
else q[!cur].push({nx, ny});
used[nx][ny] = 1;
}
}
cur = !cur;
}
cout << ans << '\n';
}
