#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,i,st,dr;
int a[5000001],deque[5000001];
long long rez;
int main()
{
	f>>n>>k;
	for(i=1;i<=n;++i)
		f>>a[i];
	st=1;dr=0;
	for(i=1;i<=n;++i)
	{
		while(st<=dr && a[i]<=a[deque[dr]])
			--dr;
		deque[++dr]=i;
		if(deque[st]==(i-k))
			st++;
		if(i>=k)
			rez+=a[deque[st]];
	}
	g<<rez;
}