#include <iostream>
#include <fstream>
#include <stack>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <stack>
#include <deque>

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

#define ll long long
#define pb push_back
const int inf = 1e9 + 5;
const int NMax = 2e5 + 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;

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

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

    for (int i=K;i <= N;++i) {
        int val;
        in>>val;

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

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

        ans += deq.front().val;
    }

    out<<ans<<'\n';

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