#include <bits/stdc++.h>
using namespace std;
int dp[2005][5], ans;
int main() {
  int n, a[2005];
  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][0] = dp[i - 1][0] + 1;
      dp[i][1] = dp[i - 1][1];
      dp[i][2] = max(dp[i - 1][1], dp[i - 1][2]) + 1;
      dp[i][3] = dp[i - 1][3];
    }
    if (a[i] == 2) {
      dp[i][0] = dp[i - 1][0];
      dp[i][1] = max(dp[i - 1][0], dp[i - 1][1]) + 1;
      dp[i][2] = dp[i - 1][2];
      dp[i][3] = max(dp[i - 1][2], dp[i - 1][3]) + 1;
    }
  }
  ans = max(dp[n][0], max(dp[n][1], max(dp[n][2], dp[n][3])));
  cout << ans;
}
