#include <fstream>
#include <deque>

using namespace std;

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

int n, k, x, xmin, B[5000000];
long long s;
deque<int> A;

int main()
{
    fin >> n >> k;
    for(int i = 0; i < n; i++)
    {
        fin>>B[i];
        while(B[i] < B[A.back()] && A.empty() == false) A.pop_back();
        A.push_back(i);
        if(i - A.front() + 1 > k && A.size()) A.pop_front();
        if(i >= k-1 && A.size()) s+= B[A.front()];
    }
    fout << s;
    return 0;
}