#include <bits/stdc++.h>
using namespace std;
long long int arr[100001], sum1[100001], sum2[100001];
int main() {
  ios::sync_with_stdio(false);
  ;
  cin.tie(0);
  ;
  long long int i, j, n, ans = -1000000000000, maxi, l, r;
  cin >> n;
  for (i = 1; i <= n; i++) {
    cin >> arr[i];
    sum1[i] = sum1[i - 1] + (arr[i] == 1);
    sum2[i] = sum2[i - 1] + (arr[i] == 2);
  }
  ans = sum1[n];
  ans = max(ans, sum2[n]);
  for (i = 1; i <= n; i++) ans = max(ans, sum1[i] + sum2[n] - sum2[i]);
  for (l = 1; l <= n; l++) {
    maxi = -1000000000000;
    for (r = l; r <= n; r++) {
      maxi = max(maxi, sum2[r] - sum1[r]);
      ans = max(ans,
                sum1[l - 1] + sum2[n] - sum2[r] + sum1[r] - sum2[l - 1] + maxi);
    }
  }
  cout << ans;
  return 0;
}
