#include <bits/stdc++.h>
using namespace std;
static inline void canhazfast() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
}
template <typename T>
T gcd(T a, T b) {
  return b == 0 ? a : gcd(b, a % b);
}
int main() {
  canhazfast();
  static int a[2000 + 1];
  static int f[2000 + 2][2], b[2000 + 2][2];
  int n;
  int ans = 0;
  cin >> n;
  for (int i = 1; i <= n; ++i) cin >> a[i];
  for (int i = 1; i <= n; ++i) {
    if (a[i] == 1) {
      f[i][0] = f[i - 1][0] + 1;
      f[i][1] = f[i - 1][1];
    } else {
      f[i][0] = f[i - 1][0];
      f[i][1] = max(f[i - 1][0], f[i - 1][1]) + 1;
    }
  }
  for (int i = n; i > 0; --i) {
    if (a[i] == 1) {
      b[i][0] = max(b[i + 1][0], b[i + 1][1]) + 1;
      b[i][1] = b[i + 1][1];
    } else {
      b[i][0] = b[i + 1][0];
      b[i][1] = b[i + 1][1] + 1;
    }
  }
  for (int r = n; r > 0; --r) {
    int c[2] = {};
    int prev[2] = {};
    int next[2];
    for (int l = r; l > 0; --l) {
      ++c[a[l] - 1];
      if (a[l] == 1) {
        next[0] = prev[0] + 1;
        next[1] = prev[1];
      } else {
        next[0] = prev[0];
        next[1] = max(prev[0], prev[1]) + 1;
      }
      ans = max(ans, f[l - 1][0] + c[0] + max(b[r + 1][0], b[r + 1][1]));
      ans = max(ans, f[l - 1][0] + next[1] + b[r + 1][1]);
      ans = max(ans, max(f[l - 1][0], f[l - 1][1]) + c[1] + b[r + 1][1]);
      prev[0] = next[0];
      prev[1] = next[1];
    }
  }
  cout << ans << '\n';
  return 0;
}
