program nunta;
var f,g:Text;
    n,a,b,c,i:longint;
begin
assign(f,'nunta.in');
assign(g,'nunta.out');
reset(f);
rewrite(g);
read(f,n);
a:=1;
b:=1;
for i:=2 to n do
  begin
    c:=b;
    b:=a+b;
    a:=c;
  end;
write(g,b);
close(f);
close(g);
end.