def fact_memo(n):
    memo = [0] * (n+1)

    def fact(n):
        if n <= 1:
            return 1
        if memo[n] != 0:
            return memo[n]

        memo[n] = fact(n-1) + fact(n-2)
        return memo[n]

    return fact(n)

n = int(input())

print(fact_memo(n))