#include <iostream>
#include <map>
using namespace std;

map<pair<int,int>,long long> combs;

long long combination(int n, int k) {
    long long ret;
    pair<int,int> p {n,k};
    if (combs.count(p) == 0) {
        if (k == 0 || k == n)
            ret = 1;
        else
            ret = combination(n-1,k) + combination(n-1,k-1);
        combs[p] = ret;
    }
    ret = combs[p];
    return ret;
}

int main() {
    int n;
    cin >> n;
    long long ans = 0;
    for (int i = 0; i <= n/2; i++) {
        ans += combination(n-i,i);
    }
    cout << ans << endl;
    return 0;
}