#include <bits/stdc++.h>
using namespace std;
long double pi = 3.141592653589793238462643383279;
const long long INF = 1e18;
void bruteforce() {}
void solve() {
  long long n, k;
  cin >> n >> k;
  long long a[n + 1];
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
  }
  a[n] = LLONG_MAX;
  sort(a, a + n);
  long long cnt[n];
  for (long long i = 0; i < n; i++) {
    long long curr = 1;
    for (long long j = i + 1; j < n + 1; j++) {
      if (a[j] - a[i] <= 5) {
        curr++;
      } else {
        break;
      }
    }
    cnt[i] = curr;
  }
  long long dp[n + 1][k + 1];
  for (long long i = 0; i < n + 1; i++) {
    for (long long j = 0; j < k + 1; j++) dp[i][j] = 0;
  }
  for (long long i = 0; i < n; i++) {
    for (long long j = 0; j < k + 1; j++) {
      dp[i + 1][j] = max(dp[i + 1][j], dp[i][j]);
      if (j + 1 <= k)
        dp[i + cnt[i]][j + 1] = max(dp[i + cnt[i]][j + 1], dp[i][j] + cnt[i]);
    }
  }
  cout << dp[n][k];
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long T = 1;
  while (T--) {
    solve();
  }
  return 0;
}
