#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, i, maxx = 2, s = 1, k = 1;
  cin >> n;
  vector<int> a(n);
  for (i = 0; i < n; i++) cin >> a[i];
  a.push_back(0);
  for (i = 0; i < n; i++) {
    if (i > 0 && s > 1 && a[i] == 1 && a[i - 1] == 2) s = 1;
    if (i > 0 && k > 1 && a[i] == 2 && a[i - 1] == 1) k = 1;
    if (a[i] == 1 && a[i + 1] == 1)
      s += 1;
    else if (min(k, s) * 2 > maxx)
      maxx = min(k, s) * 2;
    if (a[i] == 2 && a[i + 1] == 2)
      k += 1;
    else if (min(k, s) * 2 > maxx)
      maxx = min(k, s) * 2;
  }
  cout << maxx;
}
