program nume;
var f,g:TEXT;
        n,m,max,x,y,c,b,s:LONGINT;
        a:array[-1..100,-1..100] of integer;
begin
assign(F,'date.in');
assign(G,'date.out');
reset(f);
rewrite(g);
read(f,n);
read(f,m);
max:=0;
for x:=1 to n do for y:=1 to m do read(f,a[x,y]);
c:=0;
b:=0;
repeat;
s:=0;
c:=c+1;
for x:=1 to c do for y:=1 to m do begin
                                 s:=s+a[x,y];
                                 end;
if(s<s*(-1)) then for x:=1 to c do for y:=1 to m do a[x,y]:=-a[x,y];
until x=c;
repeat
b:=b+1;
s:=0;
for x:=1 to n do for y:=1 to b do begin
                                        s:=s+a[x,y];
                                        end;
if(s<s*(-1)) then for x:=1 to n do for y:=1 to b do a[x,y]:=-a[x,y];
until y=b;
{b:=0;
c:=0;
repeat;
s:=0;
c:=c+1;
for x:=1 to c do for y:=1 to m do begin
                                 s:=s+a[x,y];
                                 end;
if(s<s*(-1)) then for x:=1 to c do for y:=1 to m do a[x,y]:=-a[x,y];
until x=c;
repeat
b:=b+1;
s:=0;
for x:=1 to n do for y:=1 to b do begin
                                        s:=s+a[x,y];
                                        end;
if(s<s*(-1)) then for x:=1 to n do for y:=1 to b do a[x,y]:=-a[x,y];
until y=b;}
for x:=1 to n do for y:=1 to m do max:=max+a[x,y];
write(max);
close(f);
close(g);
end.