import java.util.*;
import java.lang.*;
import java.io.*;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner in = new Scanner(System.in);
		int i, n;
		n=in.nextInt();
		i=in.nextInt();
		if (i<=n) {
			double a, s=0, a_m;
			for (int j = 0; j < n; j++) {
				a=in.nextDouble();
				if (j != i) {s+=a;}
			}
			a_m = s/(n-1);
			System.out.printf("Ответ: %.1f", a_m);
		}
		else {System.out.printf("Условие не выполнено");}
	}
}

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NSAyIDEgMiAzIDQgNQ==

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