第四个测试点错误，错误代码为：

Wrong Answer.wrong answer Too long on line 1.

#include<iostream>
#include<cstring>
using namespace std;

int main()
{

    string a;
    cin >> a ;
    int n = a.size();

    int b[n+1];

    for(int i = 0; i < n; i++){
        if(a[i] == '0' ){
            b[i] = 1;
        }
        else{
            b[i] = -1;
        }
    }

    int sum = 0, ans = -1,s_m =0;
    for(int i = 0; i < n; i++){
        sum += b[i];
        if(sum > ans){
            ans = sum;
        }
        else if(sum < 0 ){
            sum = 0;
        }
        s_m += b[i];
    }


    if( ans > 0 ){
        cout << ans;
    }
    else{
        cout << s_m;
    }

    return 0;
}