var v:array[0..1000] of longint;
i:word;
f,g:text;
begin
assign(f,'nunta.in');reset(f);
assign(g,'nunta.out');rewrite(g);
read(f,n);
for i:=1 to n do
v[i]:=v[i-1]+v[i-2];
write(g,v[n]);
close(f);
close(g);
end.