#include <bits/stdc++.h>
using namespace std;

using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;

using u128 = unsigned __int128;
using i128 = __int128;


void solve(){
	i64 n;cin>>n;
	i64 a[60]={0};
	a[0]=1;a[1]=1;
	for(int i=2;i<=n;++i){
		a[i]=a[i-1]+a[i-2];
	}
	cout<<a[n];
	
	return;
}


int main(){
	ios::sync_with_stdio(false);cin.tie(nullptr);
	
		solve();
	
	return 0;
}


















/*
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