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

using std::vector;
using std::deque;
std::ifstream in("deque.in");
std::ofstream out("deque.out");

deque<long> a;
vector<long> m;
long N,K;

long mm()
{
    long t = a[0];
    for (long i = 1; i < a.size(); ++i)
        if ( a[i] < t ) t = a[i];
    return t;
}


int main()
{
    in >> N >> K;
    long suma = 0;
    for (long i = 0; i < N; ++i) {
        long t; in >> t;
        a.push_back(t);
        if ( a.size() > K ) a.pop_front();
        if ( a.size() == K ) suma += mm();
    }
    out << suma;

    in.close();
    out.close();
    return 0;
}