Program operatii;
type vec=array[1..100000] of longint;
var v: vec;
    n: longint;
Procedure prelucrare;
var i,nr: longint;
    gata: boolean;
    t: text;
begin
     nr:=0;
     repeat
     gata:=true;
       i:=1;
         repeat
             if v[i]<>0 then
                 begin
                    gata:=false;
                    v[i]:=v[i]-1;
                    nr:=nr+1;
                     repeat
                        i:=i+1;
                        if v[i]<>0 then v[i]:=v[i]-1;
                     until v[i+1]=0;
                 end;
            i:=i+1;
         until i>=n;
    until gata;
    assign(t,'operatii.out'); rewrite(t);
    write(t,nr);
    close(t);
end;
Procedure cit_fis;
 var t: text;
     i: longint;
begin
   assign(t,'operatii.in'); reset(t);
   readln(t,n);
   for i:=1 to n do
     read(t,v[i]);
     close(t);
   prelucrare;
end;
begin
    cit_fis;
end.