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

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