var f,g:text;
    n,i:longint;
    a:array[1..1000]of longint;
begin
     assign(f,'nunta.in');
     assign(g,'nunta.out');
     reset(f);
     rewrite(g);
     read(f,n);
     a[1]:=1;
     a[2]:=2;
     for i:=3 to n do
         a[i]:=a[i-1]+a[i-2];
     write(g,a[n]);
     close(f);
     close(g);
end.