#include <bits/stdc++.h>
using namespace std;
long long n, t, twoc, onec, opt, old;
int main() {
  cin >> n;
  cin >> t;
  if (t == 1)
    onec++;
  else
    twoc++;
  old = t;
  for (int i = 1; i < n; i++) {
    cin >> t;
    if (t == 1) {
      if (old == 2)
        onec = 1;
      else
        onec++;
    } else {
      if (old == 1)
        twoc = 1;
      else
        twoc++;
    }
    opt = max(opt, min(onec, twoc));
    old = t;
  }
  cout << opt * 2;
  return 0;
}
