// No.44 DPなすごろく
#include <iostream>
#include <vector>
using namespace std;
typedef long long ll;

int main() {
    int N;
    cin >> N;
    vector<ll> dp(N + 1);
    dp[0] = 1;
    for (int i = 0; i < N; ++i) {
        if (i + 1 <= N) dp[i + 1] += dp[i];
        if (i + 2 <= N) dp[i + 2] += dp[i];
    }
    cout << dp[N] << endl;
}