import java.util.*
fun main(args: Array<String>) {
    val scan = Scanner(System.`in`)
    val N = scan.nextInt()
    val list = listOf(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)
    print(list[N])
}