#include <bits/stdc++.h>
using namespace std;
const int MAX = 2000 + 24;
int val[MAX];
int ed[MAX][3], st[MAX][3], cur[MAX][3][3];
int main() {
  int n;
  while (~scanf("%d", &n)) {
    for (int i = 1; i <= n; i++) {
      scanf("%d", &val[i]);
    }
    memset(ed, 0, sizeof(ed));
    for (int i = 1; i <= n; i++) {
      if (val[i] == 1) {
        ed[i][val[i]] = ed[i - 1][val[i]] + 1;
        ed[i][2] = ed[i - 1][2];
      } else {
        ed[i][val[i]] = max(ed[i - 1][val[i]] + 1, ed[i - 1][val[i] - 1] + 1);
        ed[i][1] = ed[i - 1][1];
      }
    }
    memset(st, 0, sizeof(st));
    for (int i = n; i > 0; i--) {
      if (val[i] == 1) {
        st[i][val[i]] = max(st[i + 1][val[i]] + 1, st[i + 1][2] + 1);
        st[i][2] = st[i + 1][2];
      } else {
        st[i][val[i]] = st[i + 1][val[i]] + 1;
        st[i][1] = st[i + 1][1];
      }
    }
    int result = 0;
    for (int i = 1; i <= n; i++) {
      memset(cur, 0, sizeof(cur));
      for (int j = i; j <= n; j++) {
        if (val[j] == 1) {
          cur[j][val[j]][1] = cur[j - 1][val[j]][1] + 1;
          cur[j][val[j]][2] =
              max(cur[j - 1][val[j]][2] + 1, cur[j - 1][2][2] + 1);
          cur[j][2][2] = cur[j - 1][2][2];
        } else {
          cur[j][val[j]][2] = cur[j - 1][val[j]][2] + 1;
          cur[j][1][1] = cur[j - 1][1][1];
          cur[j][1][2] = max(cur[j - 1][2][2], cur[j - 1][1][2]);
        }
        result = max(result, cur[j][1][1] + ed[i - 1][1] + st[j + 1][2]);
        result = max(result, cur[j][1][1] + ed[i - 1][1] + st[j + 1][1]);
        result = max(result, cur[j][1][2] + ed[i - 1][1] + st[j + 1][2]);
        result = max(result, cur[j][2][2] + ed[i - 1][2] + st[j + 1][2]);
      }
    }
    printf("%d\n", result);
  }
  return 0;
}
