# https://www.acmicpc.net/problem/2747
# boj, 2747: 피보나치 수, python3
import sys
input = sys.stdin.readline
def fibonacci(n):
# dp table 초기화
d = [0] * 46
d[1] = 1
for i in range(2, n+1):
d[i] = d[i-1] + d[i-2]
return d[n]
if __name__ == '__main__':
n = int(input())
print(fibonacci(n))