Problem Statement

There are $N$ strings arranged in a row. It is known that, for any two adjacent strings, the string to the left is lexicographically smaller than the string to the right. That is, $S_1<S_2<...<S_N$ holds lexicographically, where $S_i$ is the $i$-th string from the left.

At least how many different characters are contained in $S_1,S_2,...,S_N$, if the length of $S_i$ is known to be $A_i$?

Constraints

• $1 \\leq N \\leq 2\\times 10^5$
• $1 \\leq A_i \\leq 10^9$
• $A_i$ is an integer.

Note

The strings do not necessarily consist of English alphabet; there can be arbitrarily many different characters (and the lexicographic order is defined for those characters).

Input

Input is given from Standard Input in the following format:

$N$ $A_1$ $A_2$ $...$ $A_N$

Output

Print the minimum possible number of different characters contained in the strings.

Sample Input 1

3
3 2 1

Sample Output 1

2

The number of different characters contained in $S_1,S_2,...,S_N$ would be $3$ when, for example, $S_1=$abc, $S_2=$bb and $S_3=$c.

However, if we choose the strings properly, the number of different characters can be $2$.

Sample Input 2

5
2 3 2 1 2

Sample Output 2

2