#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
long long powmod(long long a, long long b) {
  long long res = 1;
  a %= mod;
  assert(b >= 0);
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
void solve();
void read_input() {}
void solve() {}
int a[2005];
int left1[2005];
int right2[2005];
int dp[2005][2005][2];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  for (int i = 1; i < n; i++) {
    left1[i] = left1[i - 1];
    if (a[i - 1] == 1) {
      left1[i]++;
    }
  }
  for (int i = n; i >= 0; i--) {
    right2[i] = right2[i + 1];
    if (a[i - 1] == 2) {
      right2[i]++;
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = i; j <= n; j++) {
      int a1 = a[j - 1] == 1 ? 1 : 0;
      int a2 = a[j - 1] == 2 ? 1 : 0;
      dp[i][j][0] = max(dp[i][j - 1][0] + a1, dp[i][j - 1][1] + a2);
      dp[i][j][1] = dp[i][j - 1][1] + a2;
    }
  }
  int res = INT_MIN;
  for (int i = 1; i <= n; i++) {
    for (int j = i; j <= n; j++) {
      res = max(res,
                left1[i - 1] + right2[j + 1] + max(dp[i][j][0], dp[i][j][1]));
    }
  }
  cout << res << '\n';
  return 0;
}
