#include <bits/stdc++.h>
using namespace std;
int a[2001];
int dp[2001][4];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  for (int i = 1; i <= n; i++) {
    if (a[i] == 1) {
      dp[i][1] = dp[i - 1][1];
      dp[i][3] = dp[i - 1][3];
      dp[i][0] = dp[i - 1][0] + 1;
      dp[i][2] = max(dp[i - 1][1], dp[i - 1][2]) + 1;
    } else {
      dp[i][0] = dp[i - 1][0];
      dp[i][2] = dp[i - 1][2];
      dp[i][1] = max(dp[i - 1][0], dp[i - 1][1]) + 1;
      dp[i][3] = max(dp[i - 1][2], dp[i - 1][3]) + 1;
    }
  }
  int ans = 0;
  for (int i = 0; i < 4; i++) ans = max(ans, dp[n][i]);
  cout << ans << endl;
}
