#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
typedef long long ll;
ll n;
ll dp[55][55];
int main(void){
    cin>>n;
    dp[0][0]=1;
    for(int i=0;i<n;i++){
        for(int j=0;j<=n;j++){
            dp[i+1][j+2]+=dp[i][j];
            dp[i+1][j+1]+=dp[i][j];
        }
    }
    ll ans=0;
    for(int i=0;i<=n;i++)ans+=dp[i][n];
    cout<<ans<<endl;
}