#include <bits/stdc++.h>
using namespace std;
const int N = 2005;
int n, a[N], s1[N], s2[N], ans = 0;
void judge(int x, int y, int mid) {
  int tmp = 0;
  if (x == y)
    tmp = s1[mid] + s2[n] - s2[mid];
  else
    tmp = s1[x - 1] + s2[n] - s2[y] + s2[mid] - s2[x - 1] + s1[y] - s1[mid];
  ans = max(ans, tmp);
}
int main() {
  scanf("%d", &n);
  int i, j, x, y;
  for (i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (i = 1; i <= n; i++) {
    s1[i] = s1[i - 1];
    s2[i] = s2[i - 1];
    if (a[i] == 1)
      s1[i]++;
    else
      s2[i]++;
  }
  int mx, val, mid;
  for (x = 1; x <= n; x++) {
    if (a[x] == 1)
      val = -1;
    else
      val = 1;
    mid = x;
    mx = val;
    judge(x, x, x);
    judge(x, x, x - 1);
    for (y = x + 1; y <= n; y++) {
      if (a[y] == 1)
        val--;
      else
        val++;
      if (val > mx) mx = val, mid = y;
      judge(x, y, mid);
    }
  }
  printf("%d", ans);
  return 0;
}
