#include<cstdio>
#include<deque>
long long n,i,j,k,a[5000005],s;
using namespace std;
deque<int> c;
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%lld %lld",&n,&k);
	for (i=1;i<=n;i++) 
	{
		scanf("%lld",&a[i]);
		while ((!c.empty())&&(a[c.back()]>a[i])) c.pop_back();
		c.push_back(i);
		if (c.front()<=i-k) c.pop_front();
		if (i>=k)	s+=a[c.front()];
	}
	printf("%lld",s);
	return 0;
}