#include <iostream>
#include <cstdio>
using namespace std;
const int N=4e3+10;
struct Point {
    int x,y;
}d[4],q[2][N*N];
int h,w,ans;
int b[N][N];
bool vis[N][N];
char c[N][N];

inline bool Check(Point a) {
    return a.x>0&&a.x<h+1&&a.y>0&&a.y<w+1&&!vis[a.x][a.y]&&c[a.x][a.y]!=‘.‘;
}

inline void BFS() {
    register bool wch=0;
    int sum=0,cnt=0,h[2]={1,1},t[2]={0,0};
    q[0][++t[0]]=(Point){1,1};b[1][1]=1;vis[1][1]=1;
    while (h[wch]<=t[wch]) {
        while (h[wch]<=t[wch]) {
            register Point u=q[wch][h[wch]];h[wch]++;
            for (register int i=0;i<4;i++)
                if (Check((Point){u.x+d[i].x,u.y+d[i].y})) {
                    register Point v=(Point){u.x+d[i].x,u.y+d[i].y};
                    register bool w=c[u.x][u.y]!=c[v.x][v.y];
                    ans=max(ans,b[v.x][v.y]=b[u.x][u.y]+w);
                    q[wch^w][++t[wch^w]]=v;
                    vis[v.x][v.y]=1;
                }
        }
        wch^=1;
    }
}

int main() {
    d[0]=(Point){0,1};d[1]=(Point){1,0};d[2]=(Point){0,-1};d[3]=(Point){-1,0};
    scanf("%d%d",&h,&w);
    for (register int i=1;i<=h;i++)
        scanf("%s",c[i]+1);
    BFS();
    printf("%d",ans);
}