program flipout;
type matrice=array[1..17,1..17] of longint;
var a:matrice;
    n,m:integer;
    f,g:text;
procedure citire(var a:matrice;var n,m:integer);
var i,j:integer;
begin
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;
end;
procedure noneg(var a:matrice;n,m:integer);
var  i,j:integer;
begin
for i:=1 to n do for j:= 1 to m do if a[i,j]<0 then a[i,j]:=a[i,j]*0;
end;
function suma(a:matrice;n,m:integer):longint;
var i,j:integer;
    s:longint;
begin
s:=0;
for i:=1 to n do for j:=1 to m do s:=s+a[i,j];
suma:=s;
end;
begin
assign(f,'flip.in');reset(f);
assign(g,'flip.out');rewrite(g);
citire(a,n,m);
noneg(a,n,m);
write(g,suma(a,n,m));
close(g)
end.