import logging
import sys
from inspect import currentframe

sys.setrecursionlimit(10 ** 6)
input = sys.stdin.readline

logging.basicConfig(level=logging.DEBUG)


def dbg(*args):
    id2names = {id(v): k for k, v in currentframe().f_back.f_locals.items()}
    logging.debug(
        ", ".join(id2names.get(id(arg), "???") + " = " + repr(arg) for arg in args)
    )


def rec(n):
    if memo[n] != -1:
        return memo[n]
    if n == 0:
        memo[0] = 1
        return 1
    elif n == 1:
        memo[1] = 1
        return 1
    else:
        memo[n] = rec(n - 1) + rec(n - 2)
        return rec(n - 1) + rec(n - 2)


memo = [-1] * 61


def main():

    n = int(input())
    # dp = [0] * (n + 1)
    # dp[0] = 1
    # dp[1] = 1
    # for i in range(2, n + 1):
    #     dp[i] = dp[i - 1] + dp[i - 2]
    print(rec(n))
    # print(dp[n])


if __name__ == "__main__":
    main()