program prob;
var f,g:text;
    m,n,s,max,i,j:longint;
    w:array[1..100,1..256] of integer;
begin
assign(f,'flip.in');
assign(g,'flip.out');
reset(f);
rewrite(g);
read(f,n);
read(f,m);
s:=0;
max:=-maxlongint;
for i:=1 to n do
              for j:=1 to m do begin
                               read(f,w[i,j]);
                               if w[i,j]>0 then s:=s+w[i,j];
                               if w[i,j]>max then max:=w[i,j];
                               end;
if s=0 then write(g,max)
       else write(g,s);

close(f);
close(g);
end.