var f:text;
m,n,s,i,j:longint;
a:array[1..1000,1..1000] of longint;
begin
assign(f,'flip.in');
reset(f);
readln(f,m,n);
for i:=1 to m do
begin
for j:=1 to n do
read(f,a[i,j]);
readln(f);
end;
close(f);
for i:=1 to m do
begin
s:=0;
for j:=1 to n do
s:=s+a[i,j];
if s<0 then for j:=1 to n do
a[i,j]:=-a[i,j];
end;
for j:=1 to n do
begin
s:=0;
for i:=1 to m do
s:=s+a[i,j];
if s<0 then for i:=1 to m do
a[i,j]:=-a[i,j];
end;
s:=0;
for i:=1 to m do
for j:=1 to n do
s:=s+a[i,j];
assign(f,'flip.out');
rewrite(f);
write(f,s);
close(f);
end.