#include<iostream>
#include<algorithm>
#define INF (1<<30)
using namespace std;

int n;
long long dp[51];

int main(){
	cin>>n;
	dp[0]=1;
	dp[1]=1;
	for(int i=2;i<=n;i++){
		dp[i]=dp[i-2]+dp[i-1];
	}
	cout<<dp[n]<<endl;;
	return 0;
}