program kira;
var f,g:text;
    a:array [1..100,1..100] of integer;
    n,m,i,j:longint;
    k:int64;
begin
    assign(f,'flip.in'); reset(f);   k:=0;
    read(f,n); readln(f,m);
    for i:=1 to n do begin
        for j:=1 to m do begin read(f,a[i,j]);
        if a[i,j]>=0 then k:=k+a[i,j];
        end;
    readln(f);
    end;
    close(f);
    assign(g,'flip.out'); rewrite(g);
    write(g,k);
    close(g);
end.