import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;

public class Main {
	static InputStream is;
	static PrintWriter out;
	static String INPUT = "";
	
	static void solve()
	{
		int n = ni(), m = ni();
		int[][] a = new int[n][];
		for(int i = 0;i < n;i++){
			a[i] = na(m);
		}
		
		int[][] pre = new int[n+m][n+m];
		int[][] cur = new int[n+m][n+m];
		for(int i = 0;i < n+m;i++){
			Arrays.fill(pre[i], Integer.MIN_VALUE / 2);
			Arrays.fill(cur[i], Integer.MIN_VALUE / 2);
		}
		pre[m-1][m-1] = a[0][0];
		for(int i = 1;i < n+m-1;i++){
			for(int k = 0;k < n+m;k++){
				int rk = (i+k-(m-1));
				int ck = (i-(k-(m-1)));
				if(!((rk&1) == 0 && (ck&1) == 0))continue;
				rk /= 2; ck /= 2;
				for(int l = 0;l < n+m;l++){
					int rl = (i+l-(m-1));
					int cl = (i-(l-(m-1)));
					if(!((rl&1) == 0 && (cl&1) == 0))continue;
					rl /= 2; cl /= 2;
					int z = 0;
					for(int u = k-1;u <= k+1;u++){
						for(int v = l-1;v <= l+1;v++){
							if(u >= 0 && u < n+m && v >= 0 && v < n+m){
								z = Math.max(z, pre[u][v]);
							}
						}
					}
					if(z < 0){
						cur[k][l] = Integer.MIN_VALUE / 2;
						continue;
					}
					// r+c = i
					// r-c+m-1 = k
					if(rk >= 0 && rk < n && ck >= 0 && ck < m){
						z += a[rk][ck];
					}
					if(rl >= 0 && rl < n && cl >= 0 && cl < m && k != l){
						z += a[rl][cl];
					}
					cur[k][l] = z;
				}
			}
			int[][] dum = pre; pre = cur; cur = dum;
		}
		out.println(pre[n-1][n-1]);
	}
	
	public static void main(String[] args) throws Exception
	{
//		int n = 200, m = 99999;
//		Random gen = new Random();
//		StringBuilder sb = new StringBuilder();
//		sb.append(n + " ");
//		sb.append(n + " ");
//		for (int i = 0; i < n*n; i++) {
//			sb.append(gen.nextInt(100000) + " ");
//		}
//		INPUT = sb.toString();

		
		long S = System.currentTimeMillis();
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new PrintWriter(System.out);
		
		solve();
		out.flush();
		long G = System.currentTimeMillis();
		tr(G-S+"ms");
	}
	
	private static boolean eof()
	{
		if(lenbuf == -1)return true;
		int lptr = ptrbuf;
		while(lptr < lenbuf)if(!isSpaceChar(inbuf[lptr++]))return false;
		
		try {
			is.mark(1000);
			while(true){
				int b = is.read();
				if(b == -1){
					is.reset();
					return true;
				}else if(!isSpaceChar(b)){
					is.reset();
					return false;
				}
			}
		} catch (IOException e) {
			return true;
		}
	}
	
	private static byte[] inbuf = new byte[1024];
	static int lenbuf = 0, ptrbuf = 0;
	
	private static int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}
	
	private static boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
//	private static boolean isSpaceChar(int c) { return !(c >= 32 && c <= 126); }
	private static int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
	
	private static double nd() { return Double.parseDouble(ns()); }
	private static char nc() { return (char)skip(); }
	
	private static String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	
	private static char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}
	
	private static char[][] nm(int n, int m)
	{
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}
	
	private static int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}
	
	private static int ni()
	{
		int num = 0, b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private static long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}
		
		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}
	
	private static void tr(Object... o) { if(INPUT.length() != 0)System.out.println(Arrays.deepToString(o)); }
}


Measured memory_bytes: 11728