#include <bits/stdc++.h>

[[nodiscard]] static inline constexpr int_fast64_t solve(const int_fast64_t N) noexcept
{
	std::array<int_fast64_t, 2> dp = { 1, 1 };
	for (int_fast32_t i = 2; i <= N; ++i)
		dp[i & 1] = dp[i & 1] + dp[(i & 1) ^ 1];

	return dp[N & 1];
}

int main()
{
	std::cin.tie(nullptr);
	std::ios::sync_with_stdio(false);
	
	int_fast32_t N;
	std::cin >> N;

	std::cout << solve(N) << '\n';
	return 0;
}