#include <iostream>
#include <unordered_map>
#include <vector>
using namespace std;
//因为要考虑 1 和 -1 抵消的情况，所以数组前面要弄一个0占位！
int main() {
    int n;
    cin >> n;
    vector<int> a(n), b(n+1,0);
    for(int i=0; i<n; ++i){
        cin >> a[i];
        a[i] = (a[i] == 0 )? -1 : 1;
    }
    for(int i=1; i<=n; ++i){
        b[i] = a[i-1] + b[i-1];
    }
    unordered_map<int, int> mp;
    int maxlen = 0;
    for(int i=0; i<=n; ++i){
        if(mp.find(b[i]) == mp.end()){
            mp[b[i]] = i;
        }else{
            maxlen = max(maxlen, i - mp[b[i]]);
        }
    }
    cout << maxlen << endl;
    return 0;
}