#include <bits/stdc++.h>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int64_t> dp(n + 1, 0);
    dp[0] = 1;
    for (int i = 0; i < n; i++) {
        dp[i + 1] += dp[i];
        if (i + 2 <= n) {
            dp[i + 2] += dp[i];
        }
    }
    cout << dp[n] << endl;
    return 0;
}