const fi='fibo.inp';
fo='fibo.out';
maxn=round(1e8);
var a: array[0..maxn] of longint;
n,i: longint;
procedure ganfibo;
var i: longint;
begin
a[0]:=0;
a[1]:=1;
for i:= 2 to n do a[i]:=a[i-1]+a[i-2];
end;
begin
assign(input,fi);
reset(input);
read(n);
close(input);
assign(output,fo);
rewrite(output);
ganfibo;
write(a[n]);
close(output);
end.