#include <bits/stdc++.h>
const double eps = 1e-10;
const float epsf = 1e-6;
using namespace std;
inline long long int __gcd(long long int a, long long int b) {
  if (a == 0 || b == 0) {
    return max(a, b);
  }
  long long int tempa, tempb;
  while (1) {
    if (a % b == 0)
      return b;
    else {
      tempa = a;
      tempb = b;
      a = tempb;
      b = tempa % tempb;
    }
  }
}
inline int compfloat(float& x, float& y) {
  if (fabs(x - y) < epsf)
    return 0;
  else if (x - y > 0)
    return 1;
  return -1;
}
inline int compdouble(double x, double y) {
  if (fabs(x - y) < eps)
    return 0;
  else if (x - y > 0)
    return 1;
  else
    return -1;
}
bool prime(long long int k) {
  for (long long int i = 2; i * i <= k; i++)
    if (k % i == 0) {
      return false;
    }
  return true;
}
void pdash(int n = 1) {
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < 30; j++) {
      cout << "-";
    }
    cout << "\n";
  }
}
long long int power(long long int x, long long int y) {
  long long int result = 1;
  while (y > 0) {
    if (y & 1) {
      result = (result * x);
    }
    y = y >> 1;
    x = (x * x);
  }
  return result;
}
long long int power(long long int x, long long int y, long long int z) {
  long long int result = 1;
  x = x % z;
  while (y > 0) {
    if (y & 1) {
      result = (result * x) % z;
    }
    y = y >> 1;
    x = (x * x) % z;
  }
  return result;
}
long long int modInverse(long long int n, long long int p) {
  return power(n, p - 2, p);
}
long long int nCrF(long long int n, long long int r, long long int p) {
  if (r == 0) return 1;
  long long int f[n + 1];
  f[0] = 1;
  for (long long int i = 1; i <= n; i++) f[i] = f[i - 1] * i % p;
  return (f[n] * modInverse(f[r], p) % p * modInverse(f[n - r], p) % p) % p;
}
void cordinate_compression(vector<int>& v) {
  vector<int> p = v;
  sort(p.begin(), p.end());
  p.erase(unique(p.begin(), p.end()), p.end());
  for (int i = 0; i < (int)((v).size()); i++)
    v[i] = (int)(lower_bound(p.begin(), p.end(), v[i]) - p.begin());
}
void main_fun(int arr[], int n) {
  int dp[4][n];
  memset(dp, 0, sizeof(dp));
  if (arr[0] == 0)
    dp[0][0] = 1;
  else
    dp[1][0] = 1;
  for (int i = 1; i < n; i++) {
    if (arr[i] == 0)
      dp[0][i] = dp[0][i - 1] + 1;
    else
      dp[0][i] = dp[0][i - 1];
  }
  for (int i = 1; i < n; i++) {
    if (arr[i] == 1)
      dp[1][i] = max(dp[1][i - 1] + 1, dp[0][i - 1] + 1);
    else
      dp[1][i] = dp[1][i - 1];
  }
  for (int i = 1; i < n; i++) {
    if (arr[i] == 0) {
      dp[2][i] = max(dp[2][i - 1] + 1, max(dp[1][i - 1] + 1, dp[0][i - 1] + 1));
    } else
      dp[2][i] = dp[2][i - 1];
  }
  for (int i = 1; i < n; i++) {
    if (arr[i] == 1) {
      dp[3][i] =
          max(dp[3][i - 1] + 1,
              max(dp[2][i - 1] + 1, max(dp[1][i - 1] + 1, dp[0][i - 1] + 1)));
    } else
      dp[3][i] = dp[3][i - 1];
  }
  int ans =
      max(dp[2][n - 1], max(dp[1][n - 1], max(dp[0][n - 1], dp[3][n - 1])));
  cout << (ans);
}
void solve() {
  int n;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
    arr[i]--;
  }
  main_fun(arr, n);
  cout << "\n";
}
int main() {
  int t = 1;
  while (t--) {
    solve();
  }
}
