#include <iostream>
#include <vector>


int main(int argc, char const* argv[]) {
    int n;

    std::cin >> n;
    std::vector<long> dp(n+100);

    dp[1] = 1;
    dp[2] = 2;

    for (int i = 3; i < n+1; i++) {
        dp[i] = dp[i-1] + dp[i-2];
    }

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