#include <iostream>
#include <fstream>

using namespace std;

int dq[5000005];

int main()
{
    ifstream in ("deque.in");
    ofstream out("deque.out");
    int n,k;
    in>>n>>k;
    long long v[n+5];
    for (int i=0;i<n;i++)
    {
        in>>v[i];
    }
    int st=0,dr=-1;
    long long s=0;
    for (int i=0;i<n;i++)
    {
        if (i>=k && dq[st]==i-k)
            st++;
        while(st<=dr && v[i]<=v[dq[dr]])
        {
            dr--;
        }
        dq[++dr]=i;
        if (i>=k-1) s+=v[dq[st]];
    }
    out<<s;
    in.close();
    out.close();
    return 0;
}