var i,n,x,y:longint;
begin
read(n);
x:=1;
y:=0;
i:=1;
while (i<=n) do begin
if i mod 2=0 then y:=x+y else x:=x+y;
inc(i);
end;
if n mod 2=0 then writeln(y) else writeln(x);
end.
var i,n,x,y:longint;
begin
read(n);
x:=1;
y:=0;
i:=1;
while (i<=n) do begin
if i mod 2=0 then y:=x+y else x:=x+y;
inc(i);
end;
if n mod 2=0 then writeln(y) else writeln(x);
end.