def read_int(): return int(input())
def read_int_list(): return list(map(int, input().split()))


def fast_doubling(i):
    if i == 0:
        return 0, 1
    elif i == 1:
        return 1, 1
    else:
        a, b = fast_doubling(i >> 1)
        if i & 1:
            return a * a + b * b, b * (2 * a + b)
        else:
            return a * (2 * b - a), a * a + b * b


def fibonacci_number(i):
    ret, _ = fast_doubling(i)
    return ret


print(fibonacci_number((read_int())))