#include <fstream>

using namespace std;

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

int N, K;
int V[5000010], DQ[5000010];
int Front, Back;
long long sum;

int main()
{
    fin >> N >> K;

    for (int i = 1; i <= N; ++i)
        fin >> V[i];

    Front = 1;
    Back = 0;
    for (int i = 1; i <= N; ++i)
    {
        while (Front <= Back && V[i] <= V[DQ[Back]])
            --Back;
        DQ[++Back] = i;
        if (DQ[Front] == i - K)
            ++Front;

        if (i >= K)
            sum += V[DQ[Front]];
    }

    fout << sum << '\n';

    fin.close();
    fout.close();
    return 0;
}