#include <stdio.h>

long v[5000001],p[5000001];
long long s;

int main()
{
	long n,k,i,c=0,j,x,l;
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%ld%ld",&n,&k);
	v[1]=10000001;
	for (i=1;i<k+1;i++)
	{
		scanf("%ld",&x);
		++c;
		while ((x<v[c-1])&&(c>1)) {--c;}
		v[c]=x;p[c]=i;
	}
	s=v[1];
	l=1;
	for (i=i;i<n+1;i++)
	{
		if (p[l]==i-k) ++l;
		scanf("%ld",&x);
		++c;
		while ((x<v[c-1])&&(c>l)) {--c;}
		v[c]=x;p[c]=i;s+=v[l];
	}
	printf("%lld",s);
	return 0;
}