#include <iostream>
#include <vector>

int main() {
    int n;
    std::cin >> n;

    std::vector<long long> dp(n + 1, 0);
    dp[0] = 1;
    for (int i = 1; i <= n; i++) {
        if (i >= 1) dp[i] += dp[i - 1];
        if (i >= 2) dp[i] += dp[i - 2];
    }

    std::cout << dp[n] << std::endl;
    return 0;
}