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 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(dp[n])


if __name__ == "__main__":
    main()