#include <bits/stdc++.h>
using namespace std;
inline int read() {
  char c = getchar();
  int x = 0, f = 1;
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') x = (x << 3) + (x << 1) + c - '0', c = getchar();
  return x * f;
}
int n, sum1[2010], sum2[2010], a[2010], ans;
int main() {
  n = read();
  for (int i = 1; i <= n; ++i) a[i] = read();
  for (int i = 1; i <= n; ++i) sum1[i] = sum1[i - 1] + (a[i] == 1);
  for (int i = n; i >= 1; --i) sum2[i] = sum2[i + 1] + (a[i] == 2);
  for (int pos = 1; pos <= n + 1; ++pos) {
    int ans1 = 0, ans2 = 0;
    for (int l = 1; l <= pos; ++l) {
      ans1 = max(sum1[l - 1] + sum2[l] - sum2[pos], ans1);
    }
    for (int r = pos; r <= n + 1; ++r) {
      ans2 = max(sum2[r] + sum1[r - 1] - sum1[pos - 1], ans2);
    }
    ans = max(ans, ans1 + ans2);
  }
  printf("%d\n", ans);
  return 0;
}
