#include <stdio.h>
#include <deque>

using namespace std;

int main()
{
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
	int n, k, x;
	long long ans=0;
	deque <pair<int, int> >q;

	scanf("%d%d", &n, &k);
	for(int i=1; i<=n; i++)
	{
		scanf("%d", &x);
		
		while(!q.empty()&& x<q.back().first) {
			q.pop_back();
		}
		q.push_back(make_pair(x,i));

		if(q.front().second<=i-k)
			q.pop_front();
		if(i>=k) {
			ans+=q.front().first;
		}

	}
	printf("%lld\n", ans);
	return 0;
}