fib_DP

def fib_calc(n, memo):
    if n in memo:
        return memo[n]
    if n <= 2:
        return 1
    result = fib_calc(n-1, memo) + fib_calc(n-2, memo)
    memo[n] = result
    return result


n = int(input())


print(fib_calc(n, {}))