var fi,fo:text;
    n,i,j,max,ct:longint;
    v:array[0..1000000]of longint;
begin
  assign(fi,'operatii.in'); reset(fi);
  assign(fo,'operatii.out'); rewrite(fo);
  readln(fi,n);
  max:=-maxint;
  ct:=0;
  for i:=1 to n do
    begin
      read(fi,v[i]);
      if v[i]<>0 then
        begin
          if (max<>-maxint)and(max<v[i]) then
             begin
               inc(ct,v[i]-max);
               max:=v[i];
             end;
          if max=-maxint then
            begin
               inc(ct,v[i]-v[i-1]);
               max:=v[i];
            end;
        end
      else
       max:=-maxint;
    end;
  writeln(fo,ct);
  close(fi);
  close(fo);
end.