#include <bits/stdc++.h>

using namespace std;
ifstream in("volum.in");
ofstream out("volum.out");
const int NMAX=760;
int a[NMAX][NMAX],hmax[NMAX][NMAX];
long long dx[]={-1,1,0,0},dy[]={0,0,-1,1},n,m,rasp,h_extins;
bool seen[NMAX][NMAX];
struct poz{
    int x,y,h;
    bool operator <(const poz& aux)const{
    return aux.h<h;
    }
};
bool ok(int x,int y){
    return x>0 && x<=n && y>0 && y<=m;
}
int h_max(int x,int y){
    int maxim=0;
    if(x==1 || x==n || y==1 || y==m) return 0;
    for(int k=0;k<4;k++) {
        int xf=x+dx[k],yf=y+dy[k];
        if(ok(xf,yf))
            if(hmax[xf][yf]>0 && hmax[xf][yf]<=a[x][y])
                return 0;
            else
                maxim=max(maxim,hmax[xf][yf]-a[x][y]);

    }
    return maxim;
}
priority_queue<poz>pq;
int main()
{
    in>>n>>m;
    for(int i=1;i<=n;i++)
    for(int j=1;j<=m;j++){
        in>>a[i][j];
        if(i==1 || i==n || j==m || j==1) pq.push({i,j,a[i][j]});
    }
    while(!pq.empty()){
        int x=pq.top().x,y=pq.top().y,h=pq.top().h;
        pq.pop();
        h_extins=h_max(x,y);
        rasp+=h_extins;
        hmax[x][y]=h+h_extins;
        for(int k=0;k<4;k++){
            int xf=x+dx[k],yf=y+dy[k];
            if(ok(xf,yf) && !seen[xf][yf]){
                seen[xf][yf]=1;
                pq.push({xf,yf,a[xf][yf]});
            }
        }
    }
    out<<rasp;
    return 0;
}