String Theory

Nested quotations are useful in literature with a layered narrative, and in programming languages as well. Using a different quotation mark at every nesting level makes the levels obvious, but there is another way. A $k$-quotation marks the nesting level by repeating one single quote character, and it is defined as follows.

A 1-quotation is a string that starts with a quote character, ends with another quote character, and contains no quote character in between. This is the ordinary, unnested quotation. For example, 'this is a string' is a 1-quotation.

For $k > 1$, a $k$-quotation is a string that starts with $k$ quote characters, ends with another $k$ quote characters, and holds a nested string in between. The nested string is a non-empty sequence of $(k-1)$-quotations, and any number of non-quote characters may appear before them, between them, and after them. For example, ''All 'work' and no 'play''' is a 2-quotation.

You are given a description of a string. Find its largest possible nesting level.

The first line contains an integer $n$ ($1 \le n \le 100$). The second line contains $n$ integers $a_1, a_2, \dots, a_n$ ($1 \le a_i \le 100$), which describe a string as follows. The string starts with $a_1$ quote characters, followed by a positive number of non-quote characters, followed by $a_2$ quote characters, followed by a positive number of non-quote characters, and so on, until the string ends with $a_n$ quote characters.

Print the largest $k$ such that the described string is a $k$-quotation. If no such $k$ exists, print no quotation instead.