#include <bits/stdc++.h>
using namespace std;
const int maxn = 5100;
int n, k;
int dp[maxn][maxn];
int num[maxn];
int mx[maxn][maxn];
int main() {
  scanf("%d%d", &n, &k);
  for (int i = 1; i <= n; i++) scanf("%d", &num[i]);
  sort(num + 1, num + n + 1);
  memset(dp, -0x3f, sizeof(dp));
  dp[1][1] = 1;
  mx[1][1] = 1;
  dp[1][0] = 0;
  mx[1][0] = 0;
  int p = 1;
  int ans = 1;
  for (int i = 2; i <= n; i++) {
    for (int j = 0; j <= min(i, k); j++) {
      if (j == 0) {
        dp[i][j] = 0;
        mx[i][j] = 0;
        continue;
      }
      while (num[i] - num[p] > 5) p++;
      dp[i][j] = mx[p - 1][j - 1] + (i - p + 1);
      mx[i][j] = max(dp[i][j], mx[i - 1][j]);
      ans = max(ans, dp[i][j]);
    }
  }
  printf("%d\n", ans);
  return 0;
}
