#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000010],d[5000010];
int st,dr,n,k;
long long s;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++) fin>>v[i];
    st=1;
    dr=0;
	for (int i=1;i<=n;i++)
	{
		while (st<=dr && v[i]<=v[d[dr]]) dr--;
		d[++dr]=i;
		if(d[st]==i-k) st++;
		if(i>=k)s+=v[d[st]];
	}
	fout<<s;
    return 0;
}