INF = 10 ** 9
MOD = 10 **9 + 7
import sys
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)

def main():
    n = int(input())
    dp = [0] * (n + 1)
    dp[0] = 1
    dp[1] = 1
    for i in range(2,n + 1):
        dp[i] = dp[i - 1] + dp[i - 2]
    print(dp[n])
if __name__=='__main__':
    main()