#include <bits/stdc++.h>
using namespace std;
int n, a[2002], g[2002], f[2002];
int ans, p1, p2, s1, s2, s, sum, t;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) scanf("%d", a + i);
  for (int i = 1; i <= n; ++i) f[i] = f[i - 1] + (a[i] == 1 ? 1 : 0);
  for (int i = n; i >= 1; --i) g[i] = g[i + 1] + (a[i] == 2 ? 1 : 0);
  for (int i = 1; i <= n; ++i) {
    sum = t = 0;
    s = -n;
    p1 = p2 = i;
    s1 = s2 = 0;
    for (int j = i; j >= 1; --j) {
      if (a[j] == 1)
        t--;
      else
        t++, sum++;
      if (s < t) s = t, p1 = j, s1 = sum;
    }
    sum = t = 0;
    s = -n;
    for (int j = i + 1; j <= n; ++j) {
      if (a[j] == 2)
        t--;
      else
        t++, sum++;
      if (s < t) s = t, p2 = j, s2 = sum;
    }
    ans = max(ans, f[p1 - 1] + s1 + g[i + 1]);
    ans = max(ans, f[i] + s2 + g[p2 + 1]);
    ans = max(ans, f[p1 - 1] + s1 + s2 + g[p2 + 1]);
  }
  printf("%d", ans);
  return 0;
}
