#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <cmath>
#include <fstream>
#include <deque>
using namespace std;
ofstream out("deque.out");
ifstream in("deque.in");
int n,k,x;
deque<pair<int,int> > a;
int main(){
    in >> n >> k >> x;
    a.push_front(make_pair(x,0));
    for(int i=1;i<k;++i){
        in >> x;
        while(x <= a.back().first && !a.empty())
            a.pop_back();
        a.push_back(make_pair(x,i));
    }
    long long s = a.front().first;
    for(int i=k;i<n;++i){
        in >> x;
        while(x <= a.back().first && !a.empty())
            a.pop_back();
        a.push_back(make_pair(x,i));
        if(a.front().second<i-k+1)
            a.pop_front();
        s+=a.front().first;
    }
    out << s;
}