#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

#ifdef LOCAL
#define fin cin
#define fout cout
#else
ifstream fin("deque.in");
ofstream fout("deque.out");
#endif

int a[5000000];
deque<int> d;

int main()
{
    int n, k, s=0;
    fin >> n >> k;
    for (int i=0; i<k; i++) {
        fin >> a[i];
        while (!d.empty() && a[i] <= a[d.back()]) d.pop_back();
        d.push_back(i);
    }
    for (int i=k; i<n; i++) {
        s += a[d.front()];
        fin >> a[i];
        while (!d.empty() && d.front() <= i - k) d.pop_front();
        while (!d.empty() && a[i] <= a[d.back()]) d.pop_back();
        d.push_back(i);
    }
    s += a[d.front()];
    fout << s;
}