#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int v[5000005],coada[5000005];

int main()
{
    int n,k,i,sf=0,inc=1;
    long long s=0;

    cin>>n>>k;
    for(i=1; i<=n; i++)
    {
        cin>>v[i];
        if(i<k)
        {
            while(sf>=inc && v[i]<v[coada[sf]])
                sf--;
            sf++;
            coada[sf]=i;

        }
        else
        {
            if(i-k+1>coada[inc])
                inc++;
            while(sf>=inc && v[i]<v[coada[sf]])
                sf--;
            sf++;
            coada[sf]=i;
            s=s+v[coada[inc]];
        }

    }
    cout<<s;

    return 0;
}