#include <fstream>

using namespace std;
    ifstream cin("deque.in");
    ofstream cout("deque.out");

    struct cd
    {
        short int p;
        long long val;
    };
    cd coada[5000001];
    int v[5000001];
int main()
{
    short int n,k,inc=0,sf=0,n2;
    long long s=0;
    cin>>n>>k;
    for(n2=1;n2<=n;n2++)
    {
        cin>>v[n2];
        while(v[n2]<coada[sf].val && sf>=inc)
        {
            sf--;
        }
        sf++;
        coada[sf].val=v[n2];
        coada[sf].p=n2;
        if(coada[inc].p<n2-k+1)
        {
            inc++;
        }
        if(n2>=k)
        {
            s+=coada[inc].val;
        }
    }
    cout<<s;
    return 0;
}