#include <bits/stdc++.h>
using namespace std;
const long long inf = 0x3f3f3f3f3f3f3f3f;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
void zz() { ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0); }
int32_t main() {
  zz();
  long long n;
  cin >> n;
  vector<long long> v(n + 1, 0);
  vector<long long> cnt1(n + 1, 0), cnt2(n + 1, 0);
  for (long long i = 1; i <= n; i++) {
    cin >> v[i];
  }
  for (long long i = 1; i <= n; i++) {
    cnt1[i] = cnt1[i - 1] + (v[i] == 1);
    cnt2[i] = cnt2[i - 1] + (v[i] == 2);
  }
  long long ms = 0;
  for (long long i = 0; i <= n; i++) {
    long long ans1 = 0;
    long long ans2 = 0;
    for (long long j = 0; j <= i; j++) {
      ans1 = max(ans1, cnt1[j] + cnt2[i] - cnt2[j]);
    }
    for (long long j = i; j <= n; j++) {
      ans2 = max(ans2, cnt1[j] - cnt1[i] + cnt2[n] - cnt2[j]);
    }
    ms = max(ms, ans1 + ans2);
  }
  cout << ms << endl;
}
