#include <cstdio>
#include <deque>
using namespace std;

deque <int> deq;
int a[5000005];
long long n,i,k,smin;

int main() {
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d %d",&n,&k);
	
	
	for (i=1;i<=k;i++) {
		scanf("%d",&a[i]);
		while (!deq.empty() && a[i] <= a[deq.back()]) deq.pop_back();
		deq.push_back(i);
	}
	smin += a[deq.front()];
	
	for (i=k+1;i<=n;i++) {
		scanf("%d",&a[i]);
		while (!deq.empty() && a[i] <= a[deq.back()]) deq.pop_back();
		deq.push_back(i);
		if (deq.front() == i-k) deq.pop_front();
		smin += a[deq.front()];
	}
	printf("%lld",smin);
	return 0;
}