#include <iostream>

int main()
{
	int n;
	long long a[90] = { 2, 1, 3, 4, 7, 11, 18, 29, 47, 76, 123, 199, 322, 521, 843, 1364, 2207, 3571, 5778, 9349, 15127, 24476, 39603, 64079, 103682, 167761, 271443, 439204, 710647, 1149851, 1860498, 3010349, 4870847, 7881196, 12752043, 20633239, 33385282, 54018521, 87403803, 141422324, 228826127, 370248451, 599074578, 969323029, 1568397607, 2537720636, 4106118243, 6643838879, 10749957122, 17393796001, 28143753123, 45537549124, 73681302247, 119218851371, 192900153618, 312119004989, 505019158607, 817138163596, 1322157322203, 2139295485799, 3461452808002, 5600748293801, 9062201101803, 14662949395604, 23725150497407, 38388099893011, 62113250390418, 100501350283429, 162614600673847, 263115950957276, 425730551631123, 688846502588399, 1114577054219522, 1803423556807921, 2918000611027443, 4721424167835364, 7639424778862807, 12360848946698171, 20000273725560978, 32361122672259149, 52361396397820127, 84722519070079276, 137083915467899403, 221806434537978679, 358890350005878082, 580696784543856761, 939587134549734843, 1520283919093591604, 2459871053643326447 };

	std::cin >> n;
	std::cout << a[n];
	return 0;
}