#include <bits/stdc++.h>
using namespace std;
long long n, ans, a[2005];
long long dp[2005][2005][5];
int main() {
  cin.sync_with_stdio(0);
  cin.tie(0);
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
    --a[i];
  }
  for (int i = 1; i <= n; ++i) {
    if (a[i] == 0) {
      dp[i][i][0] = dp[i][i][2] = dp[i][i][3] = 1;
    } else {
      dp[i][i][1] = dp[i][i][2] = dp[i][i][3] = 1;
    }
    for (int j = i + 1; j <= n; ++j) {
      for (int k = 0; k <= 3; ++k) {
        dp[i][j][k] = dp[i][j - 1][k];
      }
      if (a[j] == 0) {
        dp[i][j][0] += 1;
        dp[i][j][2] = max(dp[i][j][2], dp[i][j][0]);
        dp[i][j][3] = max(dp[i][j][3] + 1, dp[i][j][1] + 1);
      } else {
        dp[i][j][1] += 1;
        dp[i][j][2] = max(dp[i][j][2] + 1, dp[i][j][0] + 1);
        dp[i][j][3] = max(dp[i][j][3], dp[i][j][1]);
      }
    }
  }
  ans = max(max(dp[1][n][0], dp[1][n][1]), dp[1][n][2]);
  for (int i = 1; i <= n; ++i) {
    for (int j = i + 1; j <= n; ++j) {
      long long L1 = 1;
      long long R1 = i - 1;
      long long L2 = i;
      long long R2 = j;
      long long L3 = j + 1;
      long long R3 = n;
      ans = max(ans, dp[L1][R1][0] + dp[L2][R2][3] + dp[L3][R3][1]);
    }
  }
  cout << ans << '\n';
}
