#include<bits/stdc++.h>
using namespace std;
int n,f[5002];
int main(){
	//freopen("b.in","r",stdin);
	//freopen("b.out","w",stdout);
	cin>>n;
	f[1]=1;
	f[2]=2;
	for(int i=3;i<=n;i++){
		f[i]=f[i-1]+f[i-2];
	}
	cout<<f[n];
	//fclose(stdin);fclose(stdout);
	return 0;
}