#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	int sn[20];
	sn[0] = 1;
	sn[1] = 1;
	sn[2] = 2;
	for(int i=3;i<=20;i++){
		sn[i] = sn[i-1]+ sn[i-2];
	}
	cin>>n;
	cout<<sn[n]<<endl;
	return 0;
}