#include <bits/stdc++.h>
using namespace std;
inline long long read() {
  register long long x = 0;
  char zf = 1;
  char ch;
  while (ch != '-' && !isdigit(ch)) ch = getchar();
  if (ch == '-') zf = -1, ch = getchar();
  while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
  return x * zf;
}
void write(long long y) {
  if (y < 0) putchar('-'), y = -y;
  if (y > 9) write(y / 10);
  putchar(y % 10 + 48);
}
void writeln(const long long y) {
  write(y);
  putchar('\n');
}
void bemin(long long &x, const long long y) {
  if (y < x) x = y;
}
void bemax(long long &x, const long long y) {
  if (y > x) x = y;
}
int i, j, k, m, n, x, y, z, cnt;
int qz[3010][3], hz[3010][3], a[3010], F[3010][3010];
int main() {
  n = read();
  for (register int i = 1; i <= n; i++) a[i] = read();
  for (register int i = 1; i <= n; i++) {
    qz[i][1] = qz[i - 1][1];
    qz[i][2] = qz[i - 1][2];
    qz[i][a[i]]++;
  }
  for (register int i = n; i >= 1; i--) {
    hz[i][1] = hz[i + 1][1];
    hz[i][2] = hz[i + 1][2];
    hz[i][a[i]]++;
  }
  for (register int i = 1; i <= n; i++)
    for (register int j = i; j <= n; j++) {
      if (a[j] == 1)
        F[i][j] = F[i][j - 1] + 1;
      else
        F[i][j] = max(F[i][j - 1], qz[j][2] - qz[i - 1][2]);
    }
  int ans = 0;
  for (register int i = 0; i <= n; i++) ans = max(ans, qz[i][1] + hz[i + 1][2]);
  for (register int i = 1; i <= n; i++)
    for (register int j = i; j <= n; j++) {
      ans = max(ans, qz[i - 1][1] + F[i][j] + hz[j + 1][2]);
    }
  cout << ans;
  return 0;
}
