#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdio>
#include<sstream>
#include<iomanip>
#include<assert.h>
#include<ctime>
#include<cstdlib>
#include<numeric>
using namespace std;
typedef long long ll;
#define loop(i,a,b) for(ll i=a;i<b;i++)
#define rloop(i,a,b) for(int i=a;i>=b;i--)
const int inf=1e8;
const ll INF=1e16;
#define MOD 1000000007
#define mod 1000000009
#define m 1000003

int main(){
	int n;
	cin>>n;
	ll dp[51];
	dp[0]=1;dp[1]=1;
	loop(i,2,n+1){
		dp[i]=dp[i-1]+dp[i-2];
	}
	cout<<dp[n]<<"\n";
}