#include<fstream>
#include<deque>

using namespace std;

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    deque <int> deq;
    int i,n,s=0,k,v[5000000];
    f>>n;
    f>>k;
    for(i=1;i<=n;i++){
        f>>v[i];
        while(deq.size() && v[i]<v[deq.back()])
            deq.pop_back();
        deq.push_back(i);
        if(deq.front()==i-k)
            deq.pop_front();
        if(i>=k)
            s+=v[deq.front()];


    }
    g<<s;
    return 0;
}