#include <bits/stdc++.h>
using namespace std;
const long long N = 2002;
const long long inf = 1e18;
long long a[N], ans[N][N][2], s[N], e[N];
int main() {
  ios_base::sync_with_stdio(false);
  long long n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  if (a[0] == 1)
    s[0] = 1;
  else
    s[0] = 0;
  for (int i = 1; i < n; i++) {
    s[i] = s[i - 1];
    if (a[i] == 1) s[i]++;
  }
  if (a[n - 1] == 2)
    e[n - 1] = 1;
  else
    e[n - 1] = 0;
  for (int i = n - 2; i >= 0; i--) {
    e[i] = e[i + 1];
    if (a[i] == 2) e[i]++;
  }
  long long mx = max(s[n - 1], e[0]);
  for (int i = 0; i < n - 1; i++) mx = max(mx, s[i] + e[i + 1]);
  for (int i = 0; i < n; i++) {
    if (a[i] == 1)
      a[i]++;
    else
      a[i]--;
  }
  for (int i = 0; i < n; i++)
    if (a[i] == 1) {
      ans[i][i][0] = 1;
      ans[i][i][1] = 1;
    } else {
      ans[i][i][0] = 0;
      ans[i][i][1] = 1;
    }
  for (int len = 2; len <= n; len++) {
    for (int i = 0; i < n; i++) {
      long long j = i + len - 1;
      if (j >= n) break;
      ans[i][j][0] = ans[i][j - 1][0];
      if (a[j] == 1) ans[i][j][0]++;
      ans[i][j][1] = ans[i][j - 1][1];
      if (a[j] == 2) ans[i][j][1]++;
      ans[i][j][1] = max(ans[i][j][0], ans[i][j][1]);
      long long val = ans[i][j][1];
      if (i != 0) val += s[i - 1];
      if (j != n) val += e[j + 1];
      mx = max(mx, val);
    }
  }
  cout << mx << endl;
}
