20251002

# import sys----------------------------ㄱ
# sys.setrecursionlimit(1000000)---------->>>>>>>파이썬 재귀 제한 푸는 코드
# def f(x):
#     if x==1:
#         return 1
#     return f(x-1)+x
# n=int(input())
# print(f(n))

# def f(x):
#     if x==1:
#         return 1
#     return f(x-1)*x
# n=int(input())
# print(f(n))

import sys
sys.setrecursionlimit(1000000)
def f(x):
    if x==2:
        return 1
    elif x==1:
        return 1
    return f(x-1)+f(x-2)
n=int(input())
print(f(n))