#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const int N = 1e6 + 5;
const int K = (1 << 17) + 10;
const long long int INF = 2e18 + 500;
const int inf = 0x7fffffff;
const int SQRT = 500;
const int lgN = 20;
int T[N], O[N];
int st[N][4];
int n;
int dp[2003][2003][3];
int A[N], B[N];
int ones(int l, int r) {
  if (l < 1 || r > n) return 0;
  return O[r] - O[l - 1];
}
int twos(int l, int r) {
  if (l < 1 || r > n) return 0;
  return T[r] - T[l - 1];
}
int flip(int l, int r) { return max(dp[l][r][1], dp[l][r][2]); }
int main(int argc, char const *argv[]) {
  cin.sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> A[i];
    B[i] = A[i];
    O[i] = O[i - 1] + (A[i] == 1);
    T[i] = T[i - 1] + (A[i] == 2);
  }
  for (int i = n; i >= 1; i--) {
    for (int j = i; j >= 1; j--) {
      dp[j][i][1] = dp[j + 1][i][1];
      dp[j][i][2] = dp[j + 1][i][2];
      if (A[j] == 1) {
        dp[j][i][1] = 1 + dp[j + 1][i][1];
      } else {
        dp[j][i][2] = 1 + max(dp[j + 1][i][1], dp[j + 1][i][2]);
      }
    }
  }
  int ans = 0;
  for (int l = 1; l <= n; l++) {
    for (int r = l; r <= n; r++) {
      ans = max(ans, ones(1, l - 1) + ones(l, r) +
                         max(ones(r + 1, n), twos(r + 1, n)));
      ans = max(ans, max(ones(1, l - 1), twos(1, l - 1)) + twos(l, r) +
                         twos(r + 1, n));
      ans = max(ans, ones(1, l - 1) + flip(l, r) + twos(r + 1, n));
    }
  }
  cout << ans << endl;
  return 0;
}
