#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
#define pb push_back
#define ll long long
#define pf push_front
const int Nmax = 5000000 + 5;
ll dq[Nmax];
ll n, k, a[Nmax], s;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; ++i) fin >> a[i];

    int fr = 1, bk = 0;
    for(int i = 1; i <= n; ++i)
    {
        while(a[i] < a[dq[bk]] && bk > 1)
            bk--;

        dq[++bk] = i;

        if(dq[fr] == i - k)fr++;

        if(i >= k)s += a[dq[fr]];
    }

    fout << s;
    return 0;
}