#include <fstream>

#define Nmax 5000100

using namespace std;

int N, K, Left = 1, Right, A[Nmax], Deque[Nmax];
long long Sum;

int main() {

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

    in >> N >> K;

    for(int i = 1; i <= N; i++) {

        in >> A[i];

        while(Left <= Right && A[i] < A[Deque[Right]])
            Right--;

        Deque[++Right] = i;

        if(Deque[Left] == i - K)
            Left++;

        if(i >= K)
            Sum += A[Deque[Left]];

        }

    out << Sum << '\n';

    in.close();
    out.close();

    return 0;
}