program operatii;
type lista=^element;
   element=record
        info:integer;
        adr:lista;
        end;
var f,g:text;
    v:array[1..1000000] of -1..1000000;
    p,n,i,j,max,x:longint;

begin
assign(f,'operatii.in');
reset(f);
p:=0;
readln(f,n);
for i:=1 to n do v[i]:=-1;
max:=0;
for i:=1 to n do
    begin
      read(f,x);
      if x>max then max:=x;
      if x>0 then
          for j:=1 to x do
                if v[j]=-1 then v[j]:=i
                           else if v[j]+1=i then v[j]:=i
                                                   else begin v[j]:=i; inc(p); end;
    end;
for i:=1 to max do
   if v[i]<>-1 then inc(p);
close(f);
assign(g,'operatii.out');
rewrite(g);
writeln(g,p);
close(g);
end.