#include <bits/stdc++.h>
using namespace std;
const int MAX = 3e3;
long long N, res, arr[MAX], inc[MAX][2], decr[MAX][2], dp[2][2];
int main() {
  ios_base::sync_with_stdio(false);
  cin >> N;
  for (int A = 1; A <= N; A++) cin >> arr[A];
  for (int A = 1; A <= N; A++) {
    inc[A][0] = inc[A - 1][0];
    inc[A][1] = inc[A - 1][1];
    if (arr[A] == 1)
      inc[A][0]++;
    else
      inc[A][1] = max(inc[A][1], inc[A - 1][0] + 1),
      inc[A][1] = max(inc[A][1], inc[A - 1][1] + 1);
    res = max(res, inc[A][0]);
    res = max(res, inc[A][1]);
  }
  for (int A = N; A >= 1; A--) {
    decr[A][0] = decr[A + 1][0];
    decr[A][1] = decr[A + 1][1];
    if (arr[A] == 1)
      decr[A][0] = max(decr[A + 1][0] + 1, decr[A + 1][1] + 1);
    else
      decr[A][1]++;
    res = max(res, decr[A][0]);
    res = max(res, decr[A][1]);
  }
  for (int A = N; A >= 1; A--) {
    for (int A = 0; A < 2; A++)
      for (int B = 0; B < 2; B++) dp[A][B] = 0;
    for (int B = A; B >= 1; B--) {
      if (arr[B] == 1) {
        dp[0][0]++;
        dp[1][0] = max(dp[1][0] + 1, dp[1][1] + 1);
      } else {
        dp[1][1]++;
        dp[0][1] = max(dp[0][1] + 1, dp[0][0] + 1);
      }
      res = max(res,
                dp[0][0] + inc[B - 1][0] + max(decr[A + 1][0], decr[A + 1][1]));
      res = max(res, dp[0][1] + inc[B - 1][0] + decr[A + 1][1]);
      res = max(res, dp[1][0] + inc[B - 1][0] + decr[A + 1][1]);
      res = max(res,
                dp[1][1] + max(inc[B - 1][0], inc[B - 1][1]) + decr[A + 1][1]);
    }
  }
  cout << res;
  return 0;
}
