#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
  vector<int> train(55, 1);
  int n;
  cin >> n;
  for (int i = 0; i < n; ++i) {
    int curr;
    cin >> curr;
    train[curr] = 0;
  }
  int j = 54;
  int maxx = 0;
  int i = 1;
  int currMax = 0;
  while (i <= 33) {
    int sum = train[i++] + train[i++] + train[i++] + train[i++] + train[j--] + train[j--];
    if (!sum)
      maxx = max(maxx, ++currMax);
    else
      currMax = 0;
  }
  cout << maxx;
  return 0;
}