#include <bits/stdc++.h>
using namespace std;
#pragma warning(disable : 4996)
#pragma comment(linker, "/STACK:336777216")
const int sqrtn = 300;
const int inf = 987654321;
const int sz = 1e5 + 5;
const int mod = 1e9 + 7;
const int N = 2005;
int n, a[N], s[N];
int one(int st, int en) {
  if (st > en) return 0;
  if (st == 0) return 0;
  return s[en] - s[st - 1];
}
int two(int st, int en) { return (en - st + 1) - one(st, en); }
int calc(int le, int ri) {
  int rlt = 0;
  for (int i = le - 1; i <= ri; i++) {
    rlt = max(rlt, one(le, i) + two(i + 1, ri));
  }
  return rlt;
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++) {
    s[i] = s[i - 1] + (a[i] == 1);
  }
  int ans = 0;
  ans = calc(1, n);
  for (int i = 1; i < n; i++) {
    ans = max(ans, calc(1, i) + calc(i + 1, n));
  }
  printf("%d\n", ans);
  return 0;
}
