package main

import . "fmt"

func main() {
	var n int
	Scan(&n)
	dp := make([]int64, n+3)
	dp[0] = 1
	for i := range dp[:n] {
		dp[i+1] += dp[i]
		dp[i+2] += dp[i]
	}
	Println(dp[n])
}