#include <bits/stdc++.h>
using namespace std;
const int N = 2000 + 5;
int n, v[N];
int a1[N];
int a2[N];
int dp21[N][N];
int dp[N];
int ap(int x, int st, int dr) {
  if (st > dr) return 0;
  if (x == 1)
    return a1[dr] - a1[st - 1];
  else
    return a2[dr] - a2[st - 1];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> v[i];
    if (v[i] == 1)
      a1[i] = 1;
    else
      a2[i] = 1;
    a1[i] += a1[i - 1];
    a2[i] += a2[i - 1];
  }
  for (int st = 1; st <= n; st++) {
    for (int dr = st; dr <= n; dr++) {
      if (v[dr] == 2)
        dp21[st][dr] = dp21[st][dr - 1];
      else {
        dp21[st][dr] = max(ap(2, st, dr), dp21[st][dr - 1]) + 1;
      }
    }
  }
  int ans = 0;
  for (int st = 1; st <= n; st++) {
    for (int dr = st; dr <= n; dr++) {
      ans = max(ans, ap(1, 1, st - 1) + dp21[st][dr] + ap(2, dr + 1, n));
    }
  }
  for (int i = 1; i <= n; i++) {
    if (v[i] == 1)
      dp[i] = dp[i - 1];
    else {
      dp[i] = max(dp[i - 1], ap(1, 1, i)) + 1;
    }
  }
  ans = max(ans, dp[n]);
  cout << ans << "\n";
  return 0;
}
