#include<bits/stdc++.h>
using namespace std;
using ll=long long;
#define rep(i,n) for(int i=0;i<n;i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
template<class T> bool chmax(T &a, T b){if (a < b){a = b;return true;} else return false;}
template<class T> bool chmin(T &a, T b){if (a > b){a = b;return true;} else return false;}

const int dx[]={1,0,-1,0},dy[]={0,1,0,-1};

int main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int H,W;
    cin>>H>>W;
    vector A(H,vector<int>(W));
    for(int i=0;i<H;i++){
        for(int j=0;j<W;j++){
            cin>>A[i][j];
        }
    }
    set<tuple<int,int,int>>s0,s1;
    s0.insert(make_tuple(A[0][1],0,1));
    s0.insert(make_tuple(A[1][0],1,0));
    s1.insert(make_tuple(A[H-1][W-2],H-1,W-2));
    s1.insert(make_tuple(A[H-2][W-1],H-2,W-1));
    vector F(H,vector<int>(W,-1));
    F[0][0]=0;
    F[H-1][W-1]=1;
    for(int t=0;;t++){
        if(t%2==0){
            if(s0.empty()){
                cout<<t<<"\n";
                return 0;
            }
            auto[c,x,y]=*s0.begin();
            s0.erase(make_tuple(c,x,y));
            F[x][y]=0;
            for(int i=0;i<4;i++){
                int ex=x+dx[i],ey=y+dy[i];
                if(0<=ex&&ex<H&&0<=ey&&ey<W&&F[ex][ey]==-1){
                    s0.insert(make_tuple(A[ex][ey],ex,ey));
                }
            }
            if(s1.count(make_tuple(c,x,y))){
                cout<<t+1<<"\n";
                return 0;
            }
        }else{
            if(s1.empty()){
                cout<<t<<"\n";
                return 0;
            }
            auto[c,x,y]=*s1.begin();
            s1.erase(make_tuple(c,x,y));
            F[x][y]=1;
            for(int i=0;i<4;i++){
                int ex=x+dx[i],ey=y+dy[i];
                if(0<=ex&&ex<H&&0<=ey&&ey<W&&F[ex][ey]==-1){
                    s1.insert(make_tuple(A[ex][ey],ex,ey));
                }
            }
            if(s0.count(make_tuple(c,x,y))){
                cout<<t+1<<"\n";
                return 0;
            }
        }
    }
}