#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const double eps = 1e-9;
const int inf = 0x3f3f3f3f;
const int maxn = 2e3 + 20;
const int maxm = 2e3 + 20;
int in(int &ret) {
  char c;
  int sgn;
  if (c = getchar(), c == EOF) return -1;
  while (c != '-' && (c < '0' || c > '9')) c = getchar();
  sgn = (c == '-') ? -1 : 1;
  ret = (c == '-') ? 0 : (c - '0');
  while (c = getchar(), c >= '0' && c <= '9') ret = ret * 10 + (c - '0');
  ret *= sgn;
  return 1;
}
int f1[maxn];
int f2[maxn];
int h1[maxn];
int h2[maxn];
int g1[maxn], g2[maxn];
int a[maxn];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) scanf("%d", &a[i]);
  for (int i = 1; i <= n; ++i) {
    if (a[i] & 1) {
      f1[i] = f1[i - 1] + 1;
      f2[i] = f2[i - 1];
    } else {
      f1[i] = f1[i - 1];
      f2[i] = max(f2[i - 1], f1[i - 1]) + 1;
    }
  }
  for (int i = n; i >= 1; --i) {
    if (a[i] & 1) {
      g2[i] = g2[i + 1];
      g1[i] = max(g2[i + 1], g1[i + 1]) + 1;
    } else {
      g2[i] = g2[i + 1] + 1;
      g1[i] = g1[i + 1];
    }
  }
  int ans = 1;
  for (int i = 1; i <= n; ++i) {
    h1[i - 1] = h2[i - 1] = 0;
    int cnt1 = 0;
    for (int j = i; j <= n; ++j) {
      if (a[j] & 1) {
        ++cnt1;
        h2[j] = h2[j - 1];
        h1[j] = max(h2[j - 1], h1[j - 1]) + 1;
      } else {
        h2[j] = h2[j - 1] + 1;
        h1[j] = h1[j - 1];
      }
      int q = f1[i - 1] + cnt1 + g1[j + 1];
      q = f1[i - 1] + h1[j] + g2[j + 1];
      ans = max(ans, q);
      q = f1[i - 1] + h2[j] + g2[j + 1];
      ans = max(ans, q);
      q = f2[i - 1] + h2[j] + g2[j + 1];
      ans = max(ans, q);
    }
  }
  printf("%d\n", ans);
  return 0;
}
