program operatii;



var v:array[1..1000000] of longint;
    ok,ok2:boolean;
    f,g:text;
    i,j,k,u,z,n:longint;

 begin
assign (f,'operatii.in');
assign (g,'operatii.out');
reset (f);
rewrite (g);
read (f,n);
for i:=1 to n do
read (f,v[i]);
i:=0;
repeat
ok2:=true;
  repeat
  i:=i+1;
  if v[i]<>0 then
    begin
    j:=i-1;
    repeat
    j:=j+1;
    ok:=false;
    if v[j]=0 then
      begin
      for k:=i to j-1 do
      v[k]:=v[k]-1;
      z:=z+1;
      ok:=true;
      i:=0;
      end;
    until (j>n) or ok;
    end;
  until ok or (i>n);
for u:=1 to n do
if v[u]<>0 then
  ok2:=false;
until ok2;

write (g,z);

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