#include <iostream>
#include <fstream>

using namespace std;

int v[10000005],d[10000005];

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