#include <bits/stdc++.h>
using namespace std;
string ANSWER[2] = {"NO\n", "YES\n"};
int v[2009], s1[2009], s2[2009];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &v[i]);
    s1[i] = s1[i - 1] + (v[i] == 1);
    s2[i] = s2[i - 1] + (v[i] == 2);
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    int a = 0, b = 0;
    for (int j = i; j <= n; j++) {
      if (v[j] == 1) b++;
      if (v[j] == 2) a++;
      if (a > b) b = a;
      ans = max(ans, s1[i - 1] + b + s2[n] - s2[j]);
    }
  }
  printf("%d\n", ans);
  return 0;
}
