#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000000000
long long dp[55];
int main() {
    
	
	dp[0] = 1;
	rep(i,50){
		dp[i+1] += dp[i];
		dp[i+2] += dp[i];
	}
	
	int n;
	cin>>n;
	
	cout<<dp[n]<<endl;
	
    return 0;
}