#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;



int main() {
    
    int N;
    cin >> N;
    
    vector< vector<long long> > dp(N+1, vector<long long>(N+1,0)  );
    dp[0][0] = 1;
    for ( int i = 0; i <= N; i++ ) {
    for ( int j = N; j >= 0; j-- ) {
        if ( dp[i][j] ) {
            if ( j+1 <= N ) { dp[i+1][j+1] += dp[i][j]; }
            if ( j+2 <= N ) { dp[i+1][j+2] += dp[i][j]; }
        }
    }
    }
    
    long long ans = 0;
    for ( int i = 1; i <= N; i++ ) {
        ans += dp[i][N];
    }
    cout << ans << endl;
    
    return 0;
}