program filip;
var f,g:text;
    n,m,i,j,s:integer;
    a:array[1..100,1..100] of integer;
begin
assign(f,'flip.in');reset(F);
assign(g,'flip.out');rewrite(g);
read(f,n,m);readln(f);
for i:=1 to n do begin
for j:=1 to m do read(f,a[i,j]);
                 read(f);
                 end;
{for i:=1 to n do begin
for j:=1 to m do write(g,a[i,j],' ');
                writeln(g);
                end;   }
s:=0;
for i:=1 to n do
for j:=1 to m do
if a[i,j]<=0 then a[i,j]:=a[i,j]*-1;
for i:=1 to n do
for j:=1 to m do
 s:=s+a[i,j];
writeln(g,s);
close(F);
close(g);
end.