Program operat;
type vec=array[1..100000] of 0..1000000;
var t: text;
    nr,max,i,q,m,n : integer;
    gasit: boolean;
    v: vec;
begin
     nr:=0;
     max:=-1;
     q:=0;
     assign(t,'operatii.in'); reset(t);
     read(t,n);
     for i:=1 to n do
         read(t,v[i]);
     q:=0;
    close(t);
       repeat
        gasit:=false;
        q:=0;
        i:=1;
          repeat
           if v[i]<>0 then
                 begin
                    gasit:=true;
                    if q=1 then nr:=nr+1;
                    nr:=nr+1;
                    v[i]:=v[i]-1;
                    repeat
                        i:=i+1;
                        v[i]:=v[i]-1;
                    until v[i+1]=0;
                    q:=1;
                 end;
              i:=i+1;
          until i>=n;
       until gasit=false;
     assign(t,'operatii.out'); rewrite(t);
       write(t,nr);
     close(t);
end.