#include <bits/stdc++.h>
using namespace std;
int A[5005], n, k, L[5005][5005], S[5005], E[5005];
void doc() {
  scanf("%d%d", &n, &k);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &A[i]);
  }
}
void xuly() {
  sort(A + 1, A + n + 1);
  for (int i = 1; i <= n; i++) {
    S[i] = 1;
    E[i] = i;
    for (int j = i - 1; j > 0; j--)
      if (A[i] - A[j] <= 5) {
        S[i]++;
        E[i] = j;
      } else
        break;
  }
  for (int i = 1; i <= k; i++) {
    for (int j = 1; j <= n; j++) {
      L[i][j] = max(max(L[i][j - 1], L[i][j]), L[i - 1][E[j] - 1] + S[j]);
    }
  }
  cout << L[k][n];
}
int main() {
  doc();
  xuly();
  return 0;
}
