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