#include<stdio.h>
int main()
{
	long long n = 0;
	long long k = 0;
	scanf("%d %d", &n,&k);
	long long arr[10000001];
	for (long long i = 0; i < n; i++)
	{
		scanf("%d ", &arr[i]);
	}
	arr[k - 1] -= arr[k - 1]*2;
	long long x = 0;
	for (long long j = 0; j < n; j++)
	{
		x = x + arr[j];
	}
	printf("%d", x);
	return 0;
}