# include <fstream>
# include <deque>
# define NMAX 5000001

using namespace std;

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

int A[NMAX];
int N, K;
long long Sum;

int main() 
{
    deque<int> Q;
    fin >> N >> K;
    for(int i = 1; i <= N; ++ i) fin >> A[i];
    for(int i = 1; i <= N; ++ i)
    {
        while(Q.size() && A[i] <= A[Q.back()])
            Q.pop_back();
        Q.push_back(i);
        if(Q.front() == i-K) Q.pop_front();
        if(i >= K) Sum += A[Q.front()];
    }
    fout << Sum << '\n';
    return 0;
}