#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int main()
{
    int n,k,v[5000005],deque[5000005];
    fin >> n >> k;
    for (int i=1;i<=n;i++)
    {
        fin >> v[i];
    }
    int front=1,back=0;
    long long s=0;
    for (int i=1;i<=n;i++)
    {
        while (front<=back && v[i]<=v[deque[back]])
        {
            back--;
        }
        back++;
        deque[back]=i;
        if (deque[front]==i-k) front++;
        if (i>=k) s+=v[deque[front]];
    }
    fout << s;
}