#include <fstream>

using namespace std;

unsigned int N, K;
int a[5000001];

int minimum[5000001];
unsigned int i, j, k, v;

long long int sol;

int main ()
{
    ifstream fin ("deque.in");
    fin >> N >> K;
    for (i=1; i<=N; i++)
        fin >> a[i];
    fin.close();
    for (i=1; i<=N-K+1; i++)
    {
        j = i + K - 1;
        minimum[++v] = a[i];
        for (k=i; k<=j; k++)
            if (a[k] < minimum[v])
                minimum[v] = a[k];
    }
    for (i=1; i<=v; i++)
        sol += minimum[i];
    ofstream fout ("deque.out");
    fout << sol;
    fout.close();
    return 0;
}