题解 | #统计每个月兔子的总数#

import sys

# for line in sys.stdin:
#     a = line.split()
#     print(int(a[0]) + int(a[1]))
n = int(input())
list = []
if n == 1:
    list= [1]
elif n == 2:
    list = [1,1]
elif n > 2:
    list = [1,1]
    # print(list[0],list[1])
    for i in range(2,n):
        list.append(list[i-1]+list[i-2])
print(list[n-1])