#include<cstdio>
#define Nmax 5000001
int n, k, a[Nmax], c[Nmax];
long long suma;
void ReadData()
{
	scanf("%d %d",&n,&k);
	for( int i=1;i<=n;i++)
	{
		scanf("%d",a+i);
	}
}
void CalcSumaMin()
{
	int prim=1, ultim = 0,i;
	for( i = 1; i<=n;i++)
	{
		while( prim <= ultim && a[i] <= a[c[ultim]])
			ultim--;
		c[++ultim]=i;

	if (c[prim] == i-k) 
		prim++;

	if (i >= k) 
		suma += a[ c[prim]];   
	}	
}

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	ReadData();
	CalcSumaMin();
	printf("%lld\n",suma);
	return 0;
}