#include<bits/stdc++.h>
using namespace std;
#define all(vec) vec.begin(),vec.end()
typedef long long int ll;
typedef pair<int,int> P;
typedef pair<P,P> PP;
const ll MOD=10000;
const ll INF=1000000010;
const int MAX=100001;
int dx[8]={0,1,0,-1,1,-1,1,-1};
int dy[8]={1,0,-1,0,1,-1,-1,1};
ll dp[60];
int main(){
	int n;cin>>n;
	dp[0]=1;
	for(int i=1;i<=n;i++){
		dp[i]+=dp[i-1];
		if(i>1)dp[i]+=dp[i-2];
	}
	cout<<dp[n]<<endl;
	return 0;
}