#include <bits/stdc++.h>

using namespace std;

long long a[5000005];
long long n, k, s;
deque <int>q;

ofstream fout("deque.out");

void Read()
{
    ifstream fin("deque.in");
    fin >> n >> k;

    int i;
    for(i = 1; i <= n; i++)
        fin >> a[i];
    fin.close();
}

void Solve()
{
    int i;
    for(i = 1; i <= k; i++)
    {
        while(!q.empty() && a[q.back()] > a[i])
            q.pop_back();
        q.push_back(i);
    }
    s += a[q.front()];

    for(i = k + 1; i <= n; i++)
    {
        while(!q.empty() && a[q.back()] > a[i])
            q.pop_back();
        q.push_back(i);
        if(i - k == q.front())q.pop_front();
        s += a[q.front()];
    }
    fout << s << "\n";
}

int main()
{
    Read();
    Solve();
    return 0;
}