#include <bits/stdc++.h>

using namespace std;

int N, K;
deque <int> dq;
vector <int> v;

int main()  {
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    cin >> N >> K;
    v.resize(N + 1);
    for(int i = 1;i <= N;i++)
        cin >> v[i];
    for(int i = 1;i <= K;i++)  {
        int val = v[i];
        while(dq.size() && v[dq.front()] >= val)
            dq.pop_front();
        dq.push_back(i);
    }
    long long sum = 0LL;
    sum += v[dq.front()];
    for(int i = K + 1;i <= N;i++)  {
        int val;
        val = v[i];
        while(dq.size() && dq.front() <= i - K)
            dq.pop_front();
        while(dq.size() && v[dq.front()] >= val)
            dq.pop_front();
        dq.push_back(i);
        cerr << dq.front() << "\n";
        sum += 1LL * v[dq.front()];
    }
    cout << sum;
    return 0;
}