#include <bits/stdc++.h>
using namespace std;
const int inf = (int)1e9;
const long long linf = (long long)1e18;
const int mod = (int)1e9 + 7;
const long double eps = (long double)1e-8;
const int maxn = (int)1e5 + 5;
const long double pi = acos(-1);
int n, a[maxn], sufs2[maxn];
int d[maxn];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (auto i = 0; i < n; ++i) {
    cin >> a[i];
  }
  for (auto i = 0; i < n; ++i) {
    int s[3];
    memset((s), 0, sizeof(s));
    d[i] = 0;
    for (auto j = i - 1; j >= 0; --j) {
      ++s[a[j]];
      d[i] = max(d[i], s[2] - s[1]);
    }
    d[i] += s[1];
  }
  memset((sufs2), 0, sizeof(sufs2));
  for (auto i = n - 1; i >= 0; --i) {
    sufs2[i] = sufs2[i + 1] + (a[i] == 2);
  }
  int ans = 0;
  for (auto i = 0; i < n; ++i) ans += (a[i] == 2);
  for (auto i = 0; i < n; ++i) {
    int s[3];
    memset((s), 0, sizeof(s));
    for (auto j = i; j < n; ++j) {
      ++s[a[j]];
      ans = max(ans, d[i] + s[1] + sufs2[j + 1]);
    }
  }
  cout << ans << endl;
  return 0;
}
