var i,s,n,h:longint;
    a,v:array[1..1000000] of longint;
    f,g:text;
function vector():longint;
 var k:longint;
     aux:byte;
begin
  k:=0;
  aux:=0;
  for i:=1 to n do
   if v[i]>a[i] then begin
     inc(a[i]);
     if aux=0 then begin
     inc(k);
     aux:=1;
     end;
     end
    else aux:=0;
   vector:=k;
end;
begin
 assign(f,'operatii.in');
 reset(f);
 readln(f,n);
 for i:=1 to n do begin
 read(f,v[i]);
 a[i]:=0;
 end;
 close(f);
 s:=0;
 repeat
  h:=vector;
  s:=s+h;
  until h=0;
 assign(g,'operatii.out');
 rewrite(g);
 write(g,s);
 close(g);
end.