#include <fstream>
#include <deque>

using namespace std;

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

const int NMAX = 5000000;
int v[NMAX + 5];
deque <int> dq;

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