#!/usr/bin/env python3

from sys import setrecursionlimit, stdin
from typing import Dict, Iterable, Set

INF: int = 2**62
MOD: int = 10**9 + 7

setrecursionlimit(10**6)


def inputs(type_=int):
    ins = input().split(' ')
    ins = [x for x in ins if x != '']

    if isinstance(type_, Iterable):
        return [t(x) for t, x in zip(type_, ins)]
    else:
        return list(map(type_, ins))


def input_(type_=int):
    a, = inputs(type_)
    return a


inputi = input_


def inputstr():
    return input_(str)


# b/aの切り上げ
def ceil(b, a):
    return (a + b - 1) // a


def answer(res) -> None:
    print(res)
    exit()


def compute():
    return

def fib(n):
    a, b = 0, 1
    for _ in range(n):
        a, b = b, a + b

    return a

def main():
    n = inputi()
    print(fib(n + 1))


if __name__ == '__main__':
    main()