package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)

func main() {
	sc.Split(bufio.ScanWords)
	n := nextInt()

	dp := make([]uint64, n+2)
	dp[0] = 1
	for i := 0; i < n; i++ {
		dp[i+1] += dp[i]
		dp[i+2] += dp[i]
	}
	fmt.Println(dp[n])
}

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	i, _ := strconv.Atoi(nextLine())
	return i
}