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#include <bits/stdc++.h>

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

int n, k;
int a[5000001];
deque<int> d;
//nr_el=0;
int main()
{
    int i=0;
    long long ans = 0;
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
        fin >> a[i];
    while(i<=n)
    {
        while(d.size()<=k)
        {
            d.push_back(i);
            i++;
        }
        int min=99999;
        for(int i=1;i<=k;i++)
        {
            if (a[d[i]]<min)
                min=a[d[i]];
        }
        ans=ans+min;
        d.pop_front();
    }
    fout<<ans;
    return 0;
}