#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
#define int unsigned long long

signed main(){
	int a;
	cin>>a;
	int f[10000];
	f[0]=1;
	f[1]=1;
	if(a==1){
		cout<<1<<"\n";
	}
	else{
		for(int i=2;i<=a;i++){
			f[i]=f[i-1]+f[i-2];
		}
	}
	cout<<f[a];

}