CF #544 div3 E. K Balanced Teams

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
typedef pair<int,int> pii;
typedef vector<int> vi;
#define check system("pause")
#define all(x) (x).begin(),(x).end()
#define de(a) cout<<#a<<" = "<<a<<endl
#define dd(a) cout<<#a<<" = "<<a<<" "
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define lowbit(a) ((a)&-(a))
#define INF 0x3f3f3f3f
const ll mod = 1e9+7;
const int N = 5e3+20;
#define dep(i,a,b) for(int i=(a);i>=(b);i--)
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define mes(p,b) memset(p,b,sizeof(p))
#define sz(x) int(x.size())
int n,k,dp[N][N],a[N],pos[N];
int main()
{
  ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
  cin>>n>>k;
  rep(i,1,n) cin>>a[i];
  sort(a+1,a+1+n);
  rep(i,1,n){
      dep(j,i,1){
          if(a[i]-a[j]<=5) pos[i]=j-1;
          else break;
      }
  }
  int ans=0;
  dp[1][1]=1;
  rep(i,1,n)
      rep(j,1,k)
        dp[i][j]=max(dp[i-1][j],dp[pos[i]][j-1]+i-pos[i]);
  rep(j,1,k) ans=max(ans,dp[n][j]); 
  cout<<ans;
  return 0;
}