#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,x,n) for(int i=x;i<n;i++)
#define ALL(v) (v).begin(),(v).end()
#define MP(a,b) make_pair(a,b)
typedef long long LL;
typedef pair<int, int> PI;
typedef vector<int> VI;
const LL MOD = 1000000007LL;
LL dp[51];
int main() {
	int N;
	cin >> N;
	dp[0] = 1;
	for (int i = 1; i <= N; i++) {
		dp[i] = dp[i - 1];
		if (i >= 2) dp[i] += dp[i - 2];
	}
	cout << dp[N] << endl;
}