#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> q;
int n, k, el, ultimul_min, v[5000005];
long long sum;

int main() {
    fin >> n >> k;
    for (int i = 1; i <= n; ++i)
        fin >> v[i];
    for (int j = 1, i = 1; j <= n; ++j) {
        if (j == n - k + 1)
            ultimul_min = v[n - k + 1];
        if (j > n - k + 1 && ultimul_min > v[j])
            ultimul_min = v[j];
        if (j > k) {
            ++i;
            if (!q.empty()) {
                sum += v[q.front()];
                while (q.front() < i) {
                    q.pop_front();
                    if (q.empty())
                        break;
                }
            }
        }
        if (!q.empty())
            while (v[j] < v[q.back()]) {
                q.pop_back();
                if (q.empty())
                    break;
            }
        q.push_back(j);
    }
    fout << sum + ultimul_min;
    return 0;
}