B. Balanced Substring time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output

You are given a string s consisting only of characters0 and 1. A substring[l, r] of s is a string s_ls_l + 1s_l + 2…s_r, and its length equals tor - l + 1. A substring is called balanced if the number of zeroes (0) equals to the number of ones in this substring.

You have to determine the length of the longest balanced substring of s.

Input

The first line contains n (1 ≤ n ≤ 100000) — the number of characters ins.

The second line contains a string s consisting of exactlyn characters. Only characters 0 and 1 can appear in s.

Output

If there is no non-empty balanced substring ins, print 0. Otherwise, print the length of the longestbalanced substring.

Examples Input

8
11010111

Output

4

Input

3
111

Output

0

Note

In the first example you can choose the substring [3, 6]. It isbalanced, and its length is 4. Choosing the substring [2, 5] is also possible.

In the second example it’s impossible to find a non-empty balanced substring.

题意：

给出一个n长度的字符串，只包含0和1，求出最长的子串，要求该子串包含的0和1的个数相同。

思路：

求出每个位置的前缀和，把0看成-1。如果两个位置的前缀和相等，计算两个位置相差的值，如果比当前答案大，则更新答案。

代码：

# -*-coding=utf-8  -*-

if __name__ =='__main__':
    a=raw_input()
    b=raw_input()
    flag=[0  for i in range(0,100005)]
    data=[-1 for i in range(0,200005)]  #data=[-1]*100005
    sum,num,ans=0,0,0
    data[0]=0
    for c in b:
        num+=1
        if c=='1':
            sum+=1
            flag[num]=sum
        else:
            sum+=-1
            flag[num]=sum
        if data[sum] == -1:
            data[sum] = num
        else:
            ans = max(ans, num - data[sum] )

    print ans

ps:最近有点膨胀，写个题目冷静下。

好好充实剩下来的一年吧。

感情的事情看缘分吧。