MyProgram:

const max=30000;
var a,b:array[1..max] of integer;
    i,n,x,y:longint;
begin
  for i:=1 to max do a[i]:=max+1;
  readln(n);
  for i:=1 to n do begin
    readln(x,y);
    if y<a[x] then a[x]:=y
  end;
  b[max]:=0;
  for i:=max-1 downto 1 do if a[i]+1>max then b[i]:=b[i+1]
    else b[i]:=b[a[i]+1]+1;
  writeln(b[1])
end.