#include <iostream>
#include <fstream>
#include <cstdlib>
#include <vector>
#include <deque>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

#define ll long long
#define pb push_back
const int NMax = 5e6 + 5;
const int inf = 1e9 + 5;

int N,K;

struct elem {
    int val,idx;
    elem (int _val = 0,int _idx = 0) {
        val = _val;
        idx = _idx;
    }
};

int main() {
    in>>N>>K;

    ll ans = 0;
    deque<elem> deq;
    for (int i=1; i<= N;++i) {
        int val;
        in>>val;

        if (deq.size() && deq.front().idx == i - K) {
            deq.pop_front();
        }

        while (deq.size() && deq.back().val >= val) {
            deq.pop_back();
        }
        deq.push_back(elem(val,i));

        if (i < K) {
            continue;
        }
        ans += deq.front().val;
    }
    out<<ans<<'\n';

    in.close();out.close();
    return 0;
}