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

typedef long long ll;

int N;

void Solve() {
    vector<ll> ways(N + 1, 0);
    ways[0] = 1;

    for (int i = 1; i <= N; i++) {
        if (i - 1 >= 0) ways[i] += ways[i - 1];
        if (i - 2 >= 0) ways[i] += ways[i - 2];
    }
    cout << ways[N] << endl;
}

int main() {
    cin >> N;

    Solve();
    return 0;
}