#include <bits/stdc++.h>
#define rep(i,a,n) for(int i=a;i<n;i++)
#define repb(i,a,b) for(int i=a;i>=b;i--)
#define all(a) a.begin(),a.end()
#define o(a) cout<<a<<endl
#define int long long
#define fi first
#define se second
using namespace std;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;

signed main(){
	int n;
	cin>>n;
	int dp[55]={};
	dp[1]=1;
	dp[2]=2;
	rep(i,3,n+1){
		dp[i]=dp[i-1]+dp[i-2];
	}
	cout<<dp[n]<<endl;
}