#include <bits/stdc++.h>
using namespace std;
vector<int> adj[2];
int dp[2003][6], sz = 0, tz = 0;
vector<int> v;
int solve(int idx, int sta) {
  if (dp[idx][sta] != -1) return dp[idx][sta];
  int e, f, g, h, p, q, r;
  vector<int>::iterator it;
  if (sta == 1 || sta == 3) {
    p = 1;
    if (adj[0][sz - 1] > idx) {
      it = upper_bound(adj[0].begin(), adj[0].end(), idx);
      h = it - adj[0].begin();
      r = adj[0][h];
      p = max(p, 1 + solve(r, sta));
    }
    if (tz > 0) {
      if (adj[1][tz - 1] > idx) {
        it = upper_bound(adj[1].begin(), adj[1].end(), idx);
        h = it - adj[1].begin();
        r = adj[1][h];
        p = max(p, 1 + solve(r, sta + 1));
      }
    }
    dp[idx][sta] = p;
    return dp[idx][sta];
  }
  if (sta == 2 || sta == 4) {
    p = 1;
    if (adj[1][tz - 1] > idx) {
      it = upper_bound(adj[1].begin(), adj[1].end(), idx);
      h = it - adj[1].begin();
      r = adj[1][h];
      p = max(p, 1 + solve(r, sta));
    }
    if (sz > 0 && sta != 4) {
      if (adj[0][sz - 1] > idx) {
        it = upper_bound(adj[0].begin(), adj[0].end(), idx);
        h = it - adj[0].begin();
        r = adj[0][h];
        p = max(p, 1 + solve(r, sta + 1));
      }
    }
    dp[idx][sta] = p;
    return dp[idx][sta];
  }
}
int main() {
  int n, i, j, k, a, b, c, ans = 0;
  scanf("%d", &n);
  for (i = 0; i < n; i++) {
    scanf("%d", &a);
    v.push_back(a);
    adj[a - 1].push_back(i);
    if (a == 1)
      sz++;
    else {
      tz++;
    }
  }
  memset(dp, -1, sizeof dp);
  for (i = 0; i < n; i++) {
    ans = max(ans, solve(i, v[i]));
  }
  printf("%d\n", ans);
  return 0;
}
