#include<bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

long long n, k, ans, v[5000005];

int main()
{
    fin >> n >> k;
    for (long long i = 1; i <= n; i++)
        fin >> v[i];
    //long long st = 1, dr = 0;
    deque<long long>dq;
    //dq.push_back(long long_MAX);
    for (long long i = 1; i <= n; i++) {
        long long ok = 1;
        while (dq.size() && ok == 1) {
            if (v[i] <= v[dq.back()])
                dq.pop_back();
            else
                ok = 0;
        }
        dq.push_back(i);
        if (i - k == dq.front())
            dq.pop_front();
        if (i >= k)
            ans += v[dq.front()];
    }

    fout << ans;
}