#include <bits/stdc++.h>
using namespace std;
int a[4], i, n, x;
int main() {
  for (cin >> n, i = 0; i < n; ++i)
    cin >> x, --x, a[0] += !x, a[1] = max(a[0], a[1] + x),
                               a[2] = max(a[1], a[2] + !x),
                               a[3] = max(a[2], a[3] + x);
  cout << a[3] << endl;
}
