var a:array[1..50,1..50] of integer;

f:array[1..100,1..50,1..50] of int64;

i,j,k,n,m:longint;

function max(a,b,c,d:int64):int64;

begin

max:=a;

if b>max then max:=b;

if c>max then max:=c;

if d>max then max:=d;

end;

begin

readln(m,n);

for i:=1 to m do

for j:=1 to n do

read(a);

f[1,1,1]:=a[1,1];

for i:=2 to m+n-1 do

for j:=2 to n do

for k:=2 to n do

if ((jk) or ((j=n) and (k=n))) and (i+2>j) and (i+2>k) then

f:=max(f+a[j,i+2-j]+a[k,i+2-k],

f+a[j,i+2-j]+a[k,i+2-k],

f+a[j,i+2-j]+a[k,i+2-k],

f+a[j,i+2-j]+a[k,i+2-k]);

writeln(f[m+n-2,n,n]);

end.