#include <bits/stdc++.h>
using namespace std;
const int maxn = 5005;
inline void read(int &x) {
  x = 0;
  int f = 1;
  char ch = 0;
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) x = (x << 3) + (x << 1) + ch - '0', ch = getchar();
  x *= f;
}
int n, k, a[maxn], dp[maxn][maxn], lp[maxn], ans = 1, mx[maxn][maxn];
int main() {
  read(n);
  read(k);
  for (register int i = 1; i <= n; ++i) read(a[i]);
  sort(a + 1, a + n + 1);
  for (register int i = 1; i <= n; ++i) {
    for (register int j = 1; j <= i; ++j) {
      lp[i] = j;
      if (a[i] - a[j] <= 5) break;
    }
  }
  for (register int i = 1; i <= n; ++i) {
    for (register int j = 1; j <= k; ++j) {
      dp[i][j] = mx[lp[i] - 1][j - 1] + i - lp[i] + 1;
      mx[i][j] = max(dp[i][j], mx[i - 1][j]);
      ans = max(ans, dp[i][j]);
    }
  }
  cout << ans;
  return 0;
}
