#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;


int main(){
  int N, K, n;
  vector<int> v;

  cin >> N >> K;
  rep(i,N){
    cin >> n;
    v.push_back(n);
  }
  sort(ALLOF(v));
  int mn = v[0];
  int mx = 0, tmp = 0, cnt = 0;
  int ii = v.size()-1;
  REP(i,K-1,v.size()){
    tmp += v[ii];
    ii--;
    cnt++;
    if(mx < tmp/(double)cnt){
      mx = tmp/(double)cnt;
    }
  }
  cout << mx - mn << endl;
  
  return 0;
}