#include <bits/stdc++.h>

#define REP(i, n) for (int i = 0; i < n; i++)
#define llINF ((long long)1e18)
#define INF ((int)1e9);
#define ALL(obj) obj.begin(), obj.end()

using namespace std;

int N;
long long memo[100];

long long rec(int n) {
    if (memo[n] != -1) return memo[n];
    if (n > N) return 0;
    if (n == N) return 1;
    long long res = rec(n + 1) + rec(n + 2);
    return memo[n] = res;
}

int main() {
    cin >> N;
    memset(memo, -1, sizeof(memo));
    cout << rec(0) << endl;
}