def fib(n,cash):
    if n==0:
        return 1
    if cash[n-1] is not None:
        return cash[n-1]
    if n==1:
        return 1
    cash[n-1]=fib(n-1,cash)+fib(n-2,cash)
    return cash[n-1]
n=int(input())
print(fib(n,[None]*n))