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