//#include<iostream>
#include<deque>
#include<fstream>
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    int k,n,i,x,sem=0;
    long long int c=0;
    deque<int> q,v;
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>x;
        sem=0;
        if(v.size()!=0)
            if(i-v.front()>=k)
            {
                q.pop_front();
                v.pop_front();
            }
        while(q.size()!=0 && sem==0)
        {
            sem=1;
            if(x<q.back())
            {
                sem=0;
                q.pop_back();
                v.pop_back();
            }
        }
        q.push_back(x);
        v.push_back(i);
        if(i>=k)
            c+=q.front();
    }
    g<<c;
    g.close();
    f.close();
    return 0;
}