#include <stdio.h>
#define N 500005
#define mare 10000000
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	int n,k,a[N],i,j,min;
	long long s=0;
	scanf("%d%d",&n,&k);
	for (i=1; i<=n; i++)
		scanf("%d",&a[i]);
	for(i=1; i<=n-k+1; i++)
	{
		min=mare;
		for (j=i; j<=i+k-1; j++)
			if (a[j]<min)
				min=a[j];
		s+=min;
	}
	printf("%lld",s);
	return 0;
}