#include <bits/stdc++.h>
#define inf 0x3f3f3f3f
#define maxn 5000010
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

int n,k;
int a[maxn];
long long s;
int i,j,p=0,best;

int main()
{
    in>>n>>k;
	best=inf;
	for(i=1;i<=n;i++)
	{
	    in>>a[i];
		if(a[i]<=best) best=a[i],p=i;
		if(p<=i-k)
		{
			best=inf,p=0;
			for(j=0;j<k;j++)
				if(a[i-j]<best) best=a[i-j],p=i-j;
		}
		if(i>=k) s+=best;
	}
	out<<s;
	return 0;
}