import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main {
	public static void main(String[] args){
		BufferedReader input
		= new BufferedReader(new InputStreamReader(System.in));
		try{
			int n = Integer.parseInt(input.readLine().trim());
			String tmp0[] = input.readLine().trim().split(" ");
			long m = Long.parseLong(input.readLine().trim());
			double[] l = new double[n];
			double min = 0;
			double max = 1e10;
			
			for(int i=0; i<n; i++){
				l[i] = Double.parseDouble(tmp0[i]);
			}
			double len = 0;
			long cut;
			for(int i=0; i<100; i++){
				len = (min+max)/2.0;
				cut = 0;
				for(int j=0; j<n; j++){
					cut += (long)(l[j]/len);
				}
				if(cut < m){
					max = len;
				}else{
					min = len;
				}
			}
			
			
			System.out.println(len);
		}catch(IOException e){
			e.printStackTrace();
		}
	}

}