#include<stdio.h>
int A[5000001], i, cap, coada, k, n, a,D[5000001];
long long s;
int main(){
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d", &n, &k);
	for(i=1;i<=n;i++) 
		scanf("%d",&A[i]);
	cap=1 ; coada=0;
	for(i=1;i<=n;i++){
		while(cap<=coada && A[i]<=A[D[coada]])
			coada--;
	A[++coada ]=i;
	if (D[cap]==i-k)cap++;
	if (i>=k) s+=A[D[cap]];
	}
	printf ("%lld", s);
	return 0;
}