#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")
using namespace std;
const long long MOD = 1e+9 + 7;
const long long INF = 0x7f7f7f7f7f7f7f7f;
const int INFi = 0x7f7f7f7f;
const long long MAXN = 1e+5 + 7;
vector<long long> adj[MAXN];
long long visit[MAXN] = {};
int dx8[] = {0, 1, 1, 1, 0, -1, -1, -1}, dy8[] = {1, 1, 0, -1, -1, -1, 0, 1};
int dx4[] = {0, 1, 0, -1}, dy4[] = {1, 0, -1, 0};
int t = 1;
long long n, cnt, i, x, y, pre, ans = 0;
void MAIN() {
  pre = 0;
  cnt = 0;
  cin >> n;
  for (i = 0; i < n; i++) {
    cin >> x;
    if (x == pre) {
      cnt++;
    } else {
      y = cnt;
      cnt = 1;
    }
    pre = x;
    ans = max(ans, 2 * (min(y, cnt)));
  }
  cout << ans;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cout << fixed;
  cout << setprecision(10);
  ;
  mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
  ;
  while (t--) {
    MAIN();
  }
}
