#include <bits/stdc++.h>
using namespace std;
const int nax = 5005;
int dp[nax][nax][2];
int a[5005];
int pref[5005];
map<int, int> m;
int main() {
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  int n, k;
  int t[5005];
  cin >> n >> k;
  for (int i = 1; n >= i; ++i) cin >> t[i], m[t[i]]++;
  sort(t + 1, t + n + 1);
  t[0] = -2;
  int ile = 1;
  for (int i = 1; n >= i; ++i) {
    while (t[i - 1] == t[i]) i++;
    if (i <= n) {
      a[ile] = t[i];
      ile++;
    }
  }
  ile--;
  for (int i = 1; ile >= i; ++i) pref[i] = pref[i - 1] + m[a[i]];
  dp[1][1][1] = m[a[1]];
  for (int i = 1; ile >= i; ++i) {
    for (int mas = 0; k >= mas; mas++) {
      for (int j = i - 1; i - 6 < j; --j) {
        if (j <= 0) continue;
        if (a[i] - a[j] <= 5 and mas >= 1)
          dp[i][mas][0] = max(dp[i][mas][0], dp[j][mas][1] + pref[i] - pref[j]);
        dp[i][mas][0] = max(dp[i][mas][0], max(dp[j][mas][0], dp[j][mas][1]));
        if (mas >= 1)
          dp[i][mas][1] =
              max(dp[i][mas][1],
                  max(dp[j][mas - 1][0], dp[j][mas - 1][1]) + m[a[i]]);
      }
    }
  }
  int ans = 0;
  for (int i = 1; k >= i; ++i)
    ans = max(ans, max(dp[ile][i][0], dp[ile][i][1]));
  cout << ans;
  return 0;
}
