#include <fstream>

using namespace std;

ifstream fin ("deque.in");
ofstream fout ("deque.out");

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

int minimum;
unsigned int i, j;

int sum;

int main ()
{
    fin >> N >> K;
    for (i=1; i<=N; i++)
        fin >> A[i];
    for (i=1; i<=N-K+1; i++)
    {
        minimum = A[i];
        for (j=i; j<=i+K-1; j++)
            if (A[j] < minimum)
                minimum = A[j];
        sum += minimum;
    }
    fout << sum << '\n';
    return 0;
}