program joculflip;
uses crt;
var f,g:text;
    a:array[1..16,1..16]of longint;
    c,p,n,m,l,k,i,j:byte;
    s,smax:longint;
begin
     assign(f,'flip.in');
     reset(f);
     assign(g,'flip.out');
     rewrite(g);
     readln(f,n,m);
     for i:=1 to n do
         begin
              for j:=1 to m do
                  read(f,a[i,j]);
              readln(f);
         end;
     s:=0;
     smax:=0;
     for i:=1 to n do
         for j:=1 to m do
             smax:=smax+a[i,j];
     p:=0;
     repeat
           p:=p+1;
           for i:=n downto p do
               begin
                    for j:=p to i do
                        for k:=1 to m do
                            a[k,j]:=a[k,j]*(-1);
                    s:=0;
                    for j:=1 to n do
                        for k:=1 to m do
                            s:=s+a[j,k];
                    if s>smax then
                            smax:=s;
                    c:=0;
                    repeat
                          c:=c+1;
                          for j:=m downto c do
                              begin
                                   for k:=c to j do
                                       for l:=1 to n do
                                           a[l,k]:=a[l,k]*(-1);
                                   s:=0;
                                   for k:=1 to n do
                                       for l:=1 to m do
                                           s:=s+a[k,l];
                                   if s>smax then
                                      smax:=s;
                                   for k:=c to j do
                                       for l:=1 to n do
                                           a[l,k]:=a[l,k]*(-1);
                              end;
                    until c=m;
                    for j:=p to i do
                        for k:=1 to m do
                            a[k,j]:=a[k,j]*(-1);
               end;
     until p=n;
     writeln(g,smax);
     close(f);
     close(g);
end.