#include<bits/stdc++.h>
typedef long long LL;
using namespace std;
const int N=10010;
const LL min_ll = -1e18;
int n, m;
LL w[N][N];
LL f[N][N][2];
inline LL mx(LL p, LL q, LL r) {
	return p > q ? (p > r ? p : r) : (q > r ? q : r);
}
inline LL dfs(int x, int y, int from) {
	if (x < 1 || x > n || y < 1 || y > m) return min_ll;
	if (f[x][y][from] != min_ll) return f[x][y][from];
	if (from == 0) f[x][y][from] = mx(dfs(x + 1, y, 0), dfs(x, y - 1, 0), dfs(x, y - 1, 1)) + w[x][y];
	else f[x][y][from] = mx(dfs(x - 1, y, 1), dfs(x, y - 1, 0), dfs(x, y - 1, 1)) + w[x][y];
	return f[x][y][from];
}
int main(void) {
	
	scanf("%d %d", &n, &m);
	for (int i = 1; i <= n; ++i)
		for (int j = 1; j <= m; ++j) {
			scanf("%lld", &w[i][j]);
			f[i][j][0] = f[i][j][1] = min_ll;
		}
	f[1][1][0] = f[1][1][1] = w[1][1];
	printf("%lld\n", dfs(n, m, 1));
	
	return 0;
}

#include<bits/stdc++.h>
#define ll long long
#define fo(i,x,y) for(register int i=x;i<=y;++i)
#define go(i,x,y) for(register int i=x;i>=y;--i)
using namespace std;
inline int read(){ int x=0,fh=1; char ch=getchar(); while(!isdigit(ch)){ if(ch=='-') fh=-1; ch=getchar(); } while(isdigit(ch)){ x=(x<<1)+(x<<3)+ch-'0'; ch=getchar(); } return x*fh; }
const int N=1005;
int a[N][N],n,m,S[N][N];
ll dp[N][N],pre[N],suf[N];
int main(){
	n=read(),m=read();
	fo(i,1,n)
		fo(j,1,m) a[i][j]=read();
	fo(j,1,m)
		fo(i,1,n) S[j][i]=S[j][i-1]+a[i][j];//每一列的前缀和 
	pre[0]=suf[n+1]=-1e17;
	//由于转移的方式是从前一列直接到后一列
	//因此第一列中除了第一行的元素其余的dp值均应赋为-inf，意为无法到达 
	fill(dp[1]+2,dp[1]+1+n,-1e17);
	dp[1][1]=a[1][1];
	fo(i,2,m+1){//按列进行转移 
		//预处理pre和suf数组 
		fo(j,1,n) pre[j]=max(pre[j-1],dp[i-1][j]-S[i-1][j]);
		go(j,n,1) suf[j]=max(suf[j+1],dp[i-1][j]+S[i-1][j-1]); 
		fo(j,1,n) dp[i][j]=max(pre[j]+S[i-1][j],suf[j]-S[i-1][j-1])+a[j][i];
	}
	cout<<dp[m+1][n];
	return 0;
}

#include <stdio.h>
 typedef long long LL;
 const LL min\_ll = -1e18; 
int n, m;
 LL w[1005][1005], f[1005][1005][2]; 
inline LL mx(LL p, LL q, LL r) {return p > q ? (p > r ? p : r) : (q > r ? q : r);} inline LL dfs(int x, int y, int from) {     if (x < 1 || x > n || y < 1 || y > m) return min\_ll;     if (f[x][y][from] != min\_ll) return f[x][y][from];     if (from == 0) f[x][y][from] = mx(dfs(x + 1, y, 0), dfs(x, y - 1, 0), dfs(x, y - 1, 1)) + w[x][y];     else f[x][y][from] = mx(dfs(x - 1, y, 1), dfs(x, y - 1, 0), dfs(x, y - 1, 1)) + w[x][y];     return f[x][y][from]; } int main(void) { //	freopen("number.in", "r", stdin); freopen("number.out", "w", stdout); 	scanf("%d %d", &n, &m); 	for (int i = 1; i <= n; ++i) 		for (int j = 1; j <= m; ++j) { 			scanf("%lld", &w[i][j]); 			f[i][j][0] = f[i][j][1] = min\_ll; 		}     f[1][1][0] = f[1][1][1] = w[1][1]; 	printf("%lld\\n", dfs(n, m, 1)); 	return 0; }