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문제

The currency system in the Kingdom of Yoax-Musty is strange and fairly inefficient. Like other countries, the kingdom has its own currencty unit denoted by K \$ (kingdom dollar). However, the Ministry of Finance issues bills for every value between 1 K \$ and (231 - 1) K \$ worth.

On the other hand, this system often enables people to make many different values just with a small number of bills. For example, if you have four bills of 1 K \$, 2 K \$, 4 K \$, and 8 K \$ worth respectively, you can make any values from 1 K #36; to 15 K \$.

In this problem, you are requested to write a program that finds the minimum value that cannot be made with a given set (multiset in a mathematical sense) of bills. For the case with the four bills (1 K \$, 2 K \$, 4 K \$, and 8 K \$), since you can make any values up to 15 K \$, your program should report 16 K $.

입력

The input consists of two lines. The first line contains an integer N (1 ≤ N ≤ 10000), the number of bills. The second line contains N integers, each of which represents the value of a bill in K \$. There may be multiple bills of the same value.

출력

Print the minimum value unable to be made on a line. The value should be given in K \$ and without any currency sign or name.

예제 입력 1

4
1 2 4 8

예제 출력 1

16

예제 입력 2

5
1 1 3 11 2

예제 출력 2

8