#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
        a[i] = a[i] == 0 ? -1 : 1;  // 将0和1转换为-1和1
    }
    
    unordered_map<int, int> sum_pos;
    int sum = 0;
    int max_len = 0;
    
    for (int i = 0; i < n; ++i) {
        sum += a[i];
        if (sum == 0) {
            max_len = i + 1;  // 从开头到当前位置满足条件
        }
        if (sum_pos.find(sum) != sum_pos.end()) {
            max_len = max(max_len, i - sum_pos[sum]);
        } else {
            sum_pos[sum] = i;
        }
    }
    
    cout << max_len << endl;
    return 0;
}