#include <bits/stdc++.h>
const int inf = 0x3f3f3f3f;
using namespace std;
int n, a[2010], pre[2010], suf[2010];
int dp[2010][2010][2];
int dpp[2010][2010][2];
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) {
      dp[i][j][0] = 0;
      dp[i][j][1] = 0;
      dpp[i][j][0] = 0;
      dpp[i][j][1] = 0;
    }
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  pre[0] = 0;
  suf[n + 1] = 0;
  for (int i = 1; i <= n; i++) {
    if (a[i] == 1)
      pre[i] = pre[i - 1] + 1;
    else
      pre[i] = pre[i - 1];
  }
  for (int i = n; i >= 1; i--) {
    if (a[i] == 2)
      suf[i] = suf[i + 1] + 1;
    else
      suf[i] = suf[i + 1];
  }
  for (int i = 1; i <= n; i++) {
    if (a[i] == 1) {
      dp[i][i][1] = 1;
      dp[i][i][0] = 0;
    } else {
      dp[i][i][1] = 0;
      dp[i][i][0] = 1;
    }
    if (a[i] == 1) {
      dpp[i][i][1] = 1;
      dpp[i][i][0] = 0;
    } else {
      dpp[i][i][1] = 0;
      dpp[i][i][0] = 1;
    }
    for (int j = i + 1; j <= n; j++) {
      if (a[j] == 2) {
        dp[i][j][0] = max(dp[i][j][0], dp[i][j - 1][0] + 1);
        dp[i][j][0] = max(dp[i][j][0], dp[i][j - 1][1] + 1);
      } else
        dp[i][j][0] = max(dp[i][j][0], dp[i][j - 1][0]);
      if (a[j] == 1)
        dp[i][j][1] = max(dp[i][j][1], dp[i][j - 1][1] + 1);
      else
        dp[i][j][1] = max(dp[i][j][1], dp[i][j - 1][1]);
      dpp[i][j][0] = max(dpp[i][j][0], suf[i] - suf[j + 1]);
      if (a[j] == 1) {
        dpp[i][j][1] = max(dpp[i][j][1], dpp[i][j - 1][1] + 1);
        dpp[i][j][1] = max(dpp[i][j][1], dpp[i][j - 1][0] + 1);
      } else
        dpp[i][j][1] = max(dpp[i][j][1], dpp[i][j - 1][1]);
    }
  }
  int ans = 1;
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++) {
      ans = max(ans, pre[j] + dp[j + 1][n][0]);
      ans = max(ans, pre[j] + dp[j + 1][n][1]);
      ans = max(ans, pre[i - 1] + dpp[i][j][0] + suf[j + 1]);
      ans = max(ans, pre[i - 1] + dpp[i][j][1] + suf[j + 1]);
      ans = max(ans, dp[0][i - 1][0] + suf[i + 1]);
      ans = max(ans, dp[0][i - 1][1] + suf[i + 1]);
    }
  cout << ans;
  return 0;
}
