#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,l,r) for(ll i=(l);i<(r);++i)

int main(){
	ll n; cin>>n;
	vector<ll> dp(n+1,0);
	dp[0]=1; dp[1]=1;
	rep(i,2,n+1){
		dp[i]=dp[i-2]+dp[i-1];
	}
	cout<<dp[n]<<endl;
}