#include <fstream>

#define NMAX 1000005

using namespace std;

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

long long ARB[4 * NMAX + 100], val, pos, stanga, dreapta, minn;

void UpdateArbore(int nod, int st, int dr)
{
    if(st == dr)
    {
        ARB[nod] = val;
        return;
    }

    int mij = (st + dr) / 2;
    if(pos <= mij)
        UpdateArbore(nod * 2, st, mij);
    else
        UpdateArbore(nod * 2 + 1, mij + 1, dr);

    ARB[nod] = min(ARB[nod * 2], ARB[nod * 2 + 1]);
}

void Query(int nod, int st, int dr)
{
    if(stanga <= st && dr <= dreapta)
    {
        if(minn > ARB[nod])
            minn = ARB[nod];
        return;
    }

    int mij = (st + dr) / 2;
    if(stanga <= mij)
        Query(nod * 2, st, mij);
    if(mij < dreapta)
        Query(nod * 2 + 1, mij + 1, dr);
}

int main()
{
    int n, m;
    fin >> n >> m;

    for(int i = 1; i <= n; ++i)
    {
        int x;
        fin >> x;

        val = x;
        pos = i;
        UpdateArbore(1, 1, n);
    }

    long long rez = 0;
    for(int i = 1; i <= n - m + 1; ++i)
    {
        minn =  10000005;
        stanga = i;
        dreapta = i + m - 1;

        Query(1, 1, n);
        rez += minn;

    }
    fout << rez << '\n';
    return 0;
}