#include<stdio.h>
#include<iostream>
#include<vector>
#include<string.h>
#include<string>
#include<algorithm>
#include<map>
using namespace std;

long long dp[100];
long long floor(int n){
		dp[0] = 1;
		dp[1] = 2;
		dp[2] = 3;
		for(int i = 3; i<n; i++){
			dp[i] = dp[i-1]+dp[i-2];
		}
		return dp[n-1];
}

int main(){
	int n;
	while(cin>>n){
		long long res = floor(n);
		cout<<res<<endl;
	}
}