#include <bits/stdc++.h>
using namespace std;
#define f first
#define s second
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, val, rez;
deque < pair < int, int > > dq;
int main()
{
    ios_base::sync_with_stdio(false);
    fin.tie(NULL), fout.tie(NULL);
    fin >> n >> k;
    for (int i = 1; i <= n; ++i)
    {
        fin >> val;
        while (!dq.empty() && val < dq.back().f)
            dq.pop_back();
        dq.push_back({val, i - 1});
        if (k == i - dq.front().s - 1)
            dq.pop_front();
        if (i >= k) rez += dq.front().f;
    }
    fout << rez;
    fin.close(), fout.close();
    return 0;
}