#include <bits/stdc++.h>
using namespace std;

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

int main() {
    int N, K; in >> N >> K;
    vector<int> V(N);
    for (int &x : V) {
        in >> x;
    }

    deque<int> DQ;
    int64_t answer = 0;
    for (int i = 0; i < N; i++) {
        if (!DQ.empty() && DQ.front() == i - K) {
            DQ.pop_front();
        }
        while (!DQ.empty() && V[DQ.back()] > V[i]) {
            DQ.pop_back();
        }
        DQ.push_back(i);
        if (i >= K - 1) {
            answer += V[DQ.front()];
        }
    }
    out << answer << "\n";

    return 0;
}