#include <bits/stdc++.h>
using namespace std;

const int MAXN = 5000005;

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

int n, k, A[MAXN], Deque[MAXN];
int Front, Back;
long long sum;

int main()
{
    fin >> n >> k;
    for (int i = 1; i <= n; ++i)
        fin >> A[i];
    Front = 1, Back = 0;
    for (int i = 1; i <= n; ++i)
    {
        while (Front <= Back && A[i] <= A[ Deque[Back] ])
            --Back;
        Deque[++Back] = i;
        if (Deque[Front] == i - k) ++Front;
        if (i >= k) sum += A[ Deque[Front] ];
    }
    fout << sum;
    fin.close(); fout.close();
    return 0;
}