#include <fstream>
using namespace std;
int v[5000001], coada[5000001];
ifstream cin("deque.in");
ofstream cout("deque.out");
int main()
{
    int n,k;
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        cin>>v[i];
    }
    int inc,sf;
    long long s=0;
    inc=sf=1;
    coada[1]=1;
    for(int i=2;i<=n;i++)
    {
        if(coada[inc]<i-k+1)
            inc++;
        while(inc<=sf and v[i]<v[coada[sf]])
        {
            sf--;
        }
        sf++;
        coada[sf]=i;
        if(i>=k)
        {
            s+=v[coada[inc]];
        }
    }
    cout<<s;
    return 0;
}