#include <stdio.h>
#define maxn 5000010
int n,k;
int a[maxn],d[maxn];
int f,b;
long long sum;
int main()
{
    freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
	int i;
	scanf("%d %d",&n,&k);
	for (i=1;i<=n;i++)
		scanf("%d",&a[i]);
	f=1;
    b=0;
    for (i=1;i<=n;i++)
    {
		while (f<=b&&a[i]<=a[d[b]])
            b--;
		d[++b] = i;
		if (d[f]==i-k)
            f++;
        if (i>=k)
            sum+=a[d[f]];
	}
	printf("%lld\n",sum);
	return 0;
}