import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

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

main()