package Yukicoder

/**
 * Created by hichikawa on 2015/11/12.
 */
fun main(args: Array<String>) {
    fun readLineLongArray(): List<Long> {
        val str = readLine() as String
        val arrStr = str.split(" ")
        val ret = arrStr.map { it.toLong() }
        return ret
    }

    fun readLineLong(): Long {
        val str = readLine() as String
        return str.toLong()
    }

    fun readLineInt(): Int {
        val str = readLine() as String
        return str.toInt()
    }

    fun readLineIntArray() : List<Int> {
        val str = readLine() as String
        val arrStr = str.split(" ")
        val ret = arrStr.map { it.toInt() }
        return ret
    }

    fun readLineDoubleArray(): List<Double> {
        val str = readLine() as String
        val arrStr = str.split(" ")
        val ret = arrStr.map { it.toDouble() }
        return ret
    }


    val num = readLineInt()
    if (num == 1) {
        println(1)
    } else if (num == 2) {
        println(2)
    } else {
        var arr = Array<Long>(num, {0})
        arr[0] = 1
        arr[1] = 1
        for (i in 2..(num-1)) {
            arr[i] = arr[i-1] + arr[i-2]
        }
        println(arr[num-1] + arr[num-2])
    }
}