var n,m,i,j,su:longint;
    sum:array[1..1000]of longint;
    a:array[1..16,1..16] of longint;
    f1,f2:text;
begin
assign(f1,'flip.in'); reset(f1);
assign(f2,'flip.out'); rewrite(f2);
read(f1,n);
read(f1,m);
for i:=1 to n do
        for j:=1 to m do
                read(f1,a[i,j]);
for j:=1 to m do
        for i:=1 to n do
                sum[j]:=sum[j]+a[i,j];
for j:=1 to m do
        if sum[j]<0 then
                for i:=1 to n do
                        a[i,j]:=a[i,j]*-1;
for j:=1 to m do
        sum[j]:=0;
for i:=1 to n do
        for j:=1 to m do
                sum[i]:=sum[i]+a[i,j];
for i:=1 to n do
        if sum[i]<0 then
                for j:=1 to m do
                        a[i,j]:=a[i,j]*-1;
for i:=1 to n do
        for j:=1 to m do
                su:=su+a[i,j];
write(f2,su);
close(f1);
close(f2);
end.