#include <bits/stdc++.h>
using namespace std;
void init_code() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
long long dp[5002][5002];
long long solve(vector<long long>& v, long long k, long long n, long long idx) {
  if (k == 0) return 0;
  if (idx >= n) return 0;
  if (dp[idx][k] != -1) return dp[idx][k];
  auto i = (upper_bound(v.begin(), v.end(), v[idx] + 5) - v.begin());
  long long cnt = i - idx;
  long long temp = solve(v, k - 1, n, i) + cnt;
  temp = max(temp, solve(v, k, n, idx + 1));
  dp[idx][k] = temp;
  return temp;
}
void solve() {
  long long n, k;
  cin >> n >> k;
  vector<long long> v(n);
  for (long long i = 0; i < n; i++) cin >> v[i];
  sort(v.begin(), v.end());
  memset(dp, -1, sizeof(dp));
  cout << solve(v, k, n, 0);
}
signed main() {
  init_code();
  long long tc = 1;
  long long num = 1;
  while (tc--) {
    num++;
    solve();
  }
}
