// bzoj1185

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstring>

#include<cstdio>

#include<cmath>

#include<queue>

#define LL long long

#define HAS 6311

#define inf 2147483640

#define Pi acos(-1.0)

#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);

using namespace std;

const int maxd=10,maxs=100010,maxh=6400;

int code[maxd],cnts[maxd],n,m;

int head[maxh],next[maxs];

int size[2],tot[2][maxs],s[2][maxs];

void decode(int st) {

	for (int i=m;i>=0;i--) code[i]=st&7,st>>=3;

}

int encode() {

	int st=0,cnt=0;

	memset(cnts,-1,sizeof(cnts));cnts[0]=0;

	for (int i=0;i<=m;i++) {

		if (cnts[code[i]]==-1) cnts[code[i]]=++cnt;

		code[i]=cnts[code[i]];

	}

	for (int i=0;i<=m;i++) st=st<<3|code[i];

	return st;

}

void shift() {

	for (int i=m;i;i--) code[i]=code[i-1];code[0]=0;

}

void add(int p,int num) {

	int st=encode();

	int id=st%HAS;

	for (int i=head[id];i;i=next[i])

		if (s[p][i]==st) {tot[p][i]=max(tot[p][i],num);return;}

	s[p][++size[p]]=st;tot[p][size[p]]=num;

	next[size[p]]=head[id];head[id]=size[p];

}

int main() {

	scanf("%d%d",&n,&m);

	int p=0,ans=-inf,val;

	size[0]=1;tot[0][1]=0;s[0][1]=0;

	for (int i=1;i<=n;i++)

		for (int j=1;j<=m;j++) {

			scanf("%d",&val);

			size[p^=1]=0;

			memset(head,0,sizeof(head));

			for (int k=1;k<=size[p^1];k++) {

				decode(s[p^1][k]);

				int left=code[j-1],up=code[j];

				if (left && up) {

					if (left==up) {

						int flag=0;

						for (int l=0;l<j-1;l++) if (code[l]) {flag=1;break;}

						for (int l=j+1;l<=m;l++) if (code[l]) {flag=1;break;}

						if (!flag) ans=max(ans,tot[p^1][k]+val);

					}

					else {

						code[j-1]=code[j]=0;

						for (int l=0;l<=m;l++) if (code[l]==up) code[l]=left;

						if (j==m) shift();

						add(p,tot[p^1][k]+val);

					}

				}

				else if (left || up) {

					int tmp=left ? left : up;

					if (j<m) {

						code[j-1]=0,code[j]=tmp;

						add(p,tot[p^1][k]+val);

					}

					if (i<n) {

						code[j-1]=tmp,code[j]=0;

						if (j==m) shift();

						add(p,tot[p^1][k]+val);

					}

				}

				else {

					if (i<n && j<m) {

						code[j-1]=code[j]=8;

						add(p,tot[p^1][k]+val);

					}

					code[j-1]=code[j]=0;

					if (j==m) shift();

					add(p,tot[p^1][k]);

				}

			}

		}

	printf("%d",ans);

	return 0;

}