#include <fstream>
#include <deque>
#include <algorithm>
#include <iostream>
#define MAX 10000000LL
using namespace std;

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

int main()
{
    ios_base::sync_with_stdio(0);
    in.tie(0);

    int n, k;
    in >> n >> k;

    long long sum = 0LL;
    deque<pair<int,int>> dq;

    for(int i = 1; i <= n; i++)
    {
        int tmp;
        in >> tmp;

        while(dq.size() && tmp <= dq.back().first) dq.pop_back();
        dq.push_back({tmp,i});

        if(dq.front().second <= i-k) dq.pop_front();

        if(i >= k) sum += dq.front().first;
    }

    out << sum;

    return 0;
}