#include <fstream>
#include <deque>
#include <vector>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

deque<long> Deque;
vector<long> V;

int main()
{
    long N,K,A;
    long long Sum=0;
    f>>N>>K;

    for(long i=0;i<N;i++)
    {
        f>>A;
        V.push_back(A);

        if(!Deque.empty() && Deque.front()<=i-K)
            Deque.pop_front();

        if (Deque.empty()) Deque.push_back(i);
                    else
                    {
                        if(V[Deque.back()]<=A) Deque.push_back(i);
                        else
                        {
                            while(V[Deque.back()]>=A && !Deque.empty()) Deque.pop_back();
                            Deque.push_back(i);
                        }
                    }
        if(i>=K-1)
            Sum+=V[Deque.front()];
    }
    g<<Sum;
    return 0;
}