program operatii;
var v:array[1..1000]of longint;
    n,i,j,nr,x,max,sw:integer;
    f,g:text;
begin
assign(f,'operatii.in'); assign(g,'operatii.out');
reset(f); rewrite(g);
readln(f,n);
max:=0;
for i:=1 to n do
begin
 read(f,v[i]);
 if v[i]>max then
  max:=v[i];
end;
x:=1;
while x<=max do
begin
 i:=1;
 while i<=n do
 begin
  if v[i]=0 then
   while v[i]=0 do
    i:=i+1;
  sw:=0;
  while v[i]>=x do
  begin
   i:=i+1;
   sw:=1;
  end;
  if sw=1 then
   nr:=nr+1;
  i:=i+1;
 end;
 x:=x+1;
end;
write(g,nr);
close(f); close(g);
end.