#include <iostream>
#include <vector>

using namespace std;

long long func(int n) {
    vector<long long> vec(51,0);
    vec.at(0) = 1;
    vec.at(1) = 1;
    for (int i = 2; i <= n; ++i) {
        vec.at(i) = vec.at(i - 1) + vec.at(i - 2);
    }
    return vec.at(n);
}

int main() {

    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int n;
    cin >> n;
    cout << func(n) << endl;
    return 0;
}