#include "bits/stdc++.h"
using namespace std;
#define rep(i,a,n) for(ll i=a;i<n;i++)
#define ALL(s) s.begin(),s.end()
#define P pair<ll,ll>
#define vl vector<ll>
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vvl vector<vector<ll>>
#define print(n) cout<<n<<endl
const int M=100010;
const int MOD=1000000007;
const int inf=1000000007;
const long long INF=1000000000000000007;
using ll=long long;


int main(){
	int n;
	cin>>n;
	ll dp[100];
	dp[0]=0,dp[1]=1,dp[2]=2;
	rep(i,3,n+1)dp[i]=dp[i-1]+dp[i-2];
	print(dp[n]);
}