#include <fstream>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int v[5000001],dq[5000001];

int main()
{
    long n,k,st,dr,sum;
    in>>n>>k;
    for(int i=0; i<n; i++) in>>v[i];
    st=0;
    dr=-1;
    sum=0;
    for(int i=0; i<n; i++)
    {
        ///scot din stanga
        if(st<=dr && dq[st]==i-k)
        {
            st++;
        }
        ///scot din dreapta
        while(st<=dr && v[i]<=v[dq[dr]])
        {
            dr--;
        }
        ///adaug i in dq
        dq[++dr]=i;
        if(i>=k-1)
        {
            sum+=v[dq[st]];
        }
    }
    out<<sum;
    return 0;
}