var f,g:text;
	n,i,ok1,nr:longint;
        ok:boolean;
	a:array[1..1000000]of longint;
procedure test;
	begin
	ok:=true;
	for i:=1 to n do
		if a[i]<>0 then begin
						ok:=false;
						break;
						end;
	end;
begin
assign(f,'operatii.in');reset(f);
assign(g,'operatii.out');rewrite(g);
readln(f,n);
for i:=1 to n do
	read(f,a[i]);
while ok=false do
	begin
	ok1:=0;
	for i:=1 to n do
	if a[i]<>0 then begin
			a[i]:=a[i]-1;
			ok1:=1;
                        if a[i+1]=0 then break;
			end;
	nr:=nr+1;
	test;
	end;
writeln(g,nr);
close(g);
end.