#include<iostream>
using namespace std;
#define MAX_VAL 100
#define int long long


signed main(){
	int N,dp[MAX_VAL] = {1,};
	cin>>N;
	
	
	for(int i = 0; i <= N; i++){
		dp[i+2] += dp[i];
		dp[i+1] += dp[i];
	}
	
	cout<<dp[N]<<endl;
	
	return 0;
}