#include <fstream>
#include <deque>

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

int N, Aux; unsigned int K; long long int Rezult;
deque<int> S;

int main()
{
    cin>>N>>K;

    while(cin>>Aux) S.push_back(Aux);

    while(S.size()>=K)
    {
        Aux=1.e20;
        for(int i=0;i<K;++i)
            if(Aux>S[i]) Aux=S[i];
        Rezult+=Aux;
        S.pop_front();
    }
    cout<<Rezult;
}