【Cf edu 30 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 characters 0 and 1. A substring [l, r] of s is a string s_ls_l + 1s_l + 2... s_r, and its length equals to r - 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 in s.

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

Output

If there is no non-empty balanced substring in s, print 0. Otherwise, print the length of the longest balanced substring.

Examples

input

811010111

output

4

input

3111

output

0

Note

In the first example you can choose the substring [3, 6]. It is balanced, 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.

 

【翻译】给出01串，求出最长连续子串使得01个数相同

 

题解：
     ①经典思想：维护差值——将0设为-1

     ②前缀和中，前缀和相同的两点可构成合法区间，直接统计最大值就是了

#include<stdio.h>
#include<algorithm>
#define go(i,a,b) for(int i=a;i<=b;i++)
using namespace std;
const int N=100004;
int n,a[N],pos[N],_[N],sum[N],ans;
int main()
{
    scanf("%d",&n);
    go(i,1,n)scanf("%1d",a+i);
    go(i,1,n)sum[i]=sum[i-1]+(a[i]?1:-1);
    go(i,1,n)if(pos[sum[i]]||sum[i]==0)
    ans=max(ans,i-pos[sum[i]]);else pos[sum[i]]=i;
    printf("%d\n",ans);return 0;
}//Paul_Guderian

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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来源：https://www.cnblogs.com/Damitu/p/7745321.html