#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
const int NMAX = 5e6 + 5;
int a[NMAX];

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

    long long ans = 0;
    deque<int> dq;
    for(int i = 1; i <= n; i++)
    {
        while(!dq.empty() && a[i] <= a[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front() == i - k)
            dq.pop_front();
        if(i >= k)
            ans += 1LL * a[dq.front()];
    }
    fout << ans;

    return 0;
}