Codeforces Round #544 (Div. 3) C. Balanced Team(upper_bound)

#include <bits/stdc++.h>
#define ll long long
using namespace std;
int n,m;
int pre[200005];

int main()
{
  scanf("%d",&n);
  for(int i=0;i<n;i++){
    scanf("%d",&pre[i]);
  }
  sort(pre, pre + n);
  int ans = 1;
  for(int i=0;i<n-1;i++){
    int cnt = upper_bound(pre, pre + n, pre[i] + 5) - pre;
    ans = max(ans, cnt - i);
  }
  cout<<ans<<endl;
  return 0;
}