#include <fstream>

using namespace std;

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

#define NMAX 5000100

int DQ[NMAX], A[NMAX], N, K, St, Dr;
long long Sum;

int main()
{
        int i;
        fin >>N >>K;
        St = 1;
        for (i = 1; i <= N; i++)
        {
                fin >>A[i];
                A[i] += 10000000;
                for (; A[i] <= A[DQ[Dr]] && Dr >= St; Dr--);
                DQ[++Dr] = i;
                if (DQ[St] <= i - K) St++;
                if (i >= K)
                        Sum += (A[DQ[St]] - 10000000);
        }
        fout <<Sum;
        fout.close();
        return 0;
}