using namespace std;
#include <iostream>
#include <fstream>
ifstream fin("kfib.in");
ofstream fout("kfib.out");
int main()
{
	long long n,a=1,b=1,k,i;
	fin>>k;
	for(i=3;i<=k;i++)
	{
		n=a+b;
		b=a;
		a=n;
	}
	fout<<n;
	return 0;
}