#include <bits/stdc++.h>

#define Nmax 5000000

using namespace std;

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

deque < int > DQ;

int N, K;
int A[Nmax + 5];
long long sum = 0;

int main()
{
    fin >> N >> K;
    for (int i = 1; i <= N; ++i)
        fin >> A[i];
    for (int i = 1; i <= N; ++i)
    {
        while (DQ.empty() == 0 && A[i] <= A[DQ.back()])
            DQ.pop_back();
        DQ.push_back(i);
        if (DQ.front() == i - K)
            DQ.pop_front();
        if (i >= K)
            sum += A[DQ.front()];
    }
    fout << sum << "\n";
    return 0;
}