#include<bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int N,K,x,s;
deque < pair<int,int> > deq;
int main()
{
    f>>N>>K>>x;
    deq.push_back(make_pair(1,x));
    for(int i=2;i<=N;++i){
        f>>x;
        while(!deq.empty()&&x<=deq.back().second)deq.pop_back();
        deq.push_back(make_pair(i,x));
        if(i-K==deq.front().first)deq.pop_front();
        if(K<=i)s+=deq.front().second;
    }
    g<<s;
    return 0;
}