#include <bits/stdc++.h>

using namespace std;

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

const int N_MAX = 5e6 + 5;

int N, K, x;
int v[N_MAX];

long long sum = 0;

deque < int > DQ;

int main()
{
    fin >> N >> K;
    for (int i = 1; i <= N; i++) {
        fin >> v[i];
    }
    for (int i = 1; i <= K; i++) {
        while (DQ.size() > 0 && v[i] < v[DQ.front()]) {
            DQ.pop_front();
        }
        DQ.push_front(i);
    }
    sum += v[DQ.back()];
    for (int i = K + 1; i <= N; i++) {
        while (DQ.size() > 0 && v[i] < v[DQ.front()]) {
            DQ.pop_front();
        }
        DQ.push_front(i);
        if (DQ.back() <= i - K) {
            DQ.pop_back();
        }
        sum += v[DQ.back()];
    }
    fout << sum << "\n";
    return 0;
}