#include <fstream>

using namespace std;

ifstream cin ("deque.in");
ofstream cout ("deque.out");
int v[5000001], st[5000001];
int main()
{
    int n,i,k, sf, inc, s=0;
    cin>>n>>k;
    for(i=1;i<=n;i++) cin>>v[i];
    st[1]=1;
    sf=1;
    inc=1;
    for(i=2;i<=n;i++)
    {
        while(sf>=inc && v[i]<=v[st[sf]])
            sf--;
        sf++;
        st[sf]=i;
        if(i>=k)
        {
            if(st[inc]<i-k+1) inc++;
            s=s+v[st[inc]];
        }
    }
    cout<<s;
    return 0;
}