def main():
    n = int(input())
    ans = solve1(n)
    print(ans)


def solve1(n):
    if n <= 1:
        return 1
    a, b = 1, 1

    for _ in range(2, n + 1):
        a, b = b, a + b
    return b

if __name__ == '__main__':
    main() def main():
    n = int(input())
    ans = solve1(n)
    print(ans) main n = int(input()) n int(input()) int input() input ans = solve1(n) ans solve1(n) solve1 n print(ans) print ans def solve1(n):
    if n <= 1:
        return 1
    a, b = 1, 1

    for _ in range(2, n + 1):
        a, b = b, a + b
    return b solve1 if n <= 1:
        return 1
     n <= 1 n 1 return 1 1 a, b = 1, 1 a 1 b 1 for _ in range(2, n + 1):
        a, b = b, a + b
     _ range(2, n + 1) range 2 n + 1 n 1 a, b = b, a + b a b b a + b a b return b b n n if __name__ == '__main__':
    main() __name__ == '__main__' __name__ '__main__' main() main def main():
    n = int(input())
    ans = solve1(n)
    print(ans) def main():
    n = int(input())
    ans = solve1(n)
    print(ans) main def solve1(n):
    if n <= 1:
        return 1
    a, b = 1, 1

    for _ in range(2, n + 1):
        a, b = b, a + b
    return b def solve1(n):
    if n <= 1:
        return 1
    a, b = 1, 1

    for _ in range(2, n + 1):
        a, b = b, a + b
    return b solve1
def main():
    n = int(input())
    ans = solve1(n)
    print(ans)


def solve1(n):
    if n <= 1:
        return 1
    a, b = 1, 1

    for _ in range(2, n + 1):
        a, b = b, a + b
    return b

if __name__ == '__main__':
    main()