#include <fstream>

#define maxn 5000005

int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;

using namespace std;

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

    fin>>N>>K;

    for (int i = 1; i <= N; i++){
        fin>>A[i];
    }

    Front = 1, Back = 0;

    for (int i = 1; i <= N; i++){
        while (Front <= Back && A[i] <= A[ Deque[Back] ]){
            Back--;
        }

        Deque[++Back] = i;

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

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

    fout<<Sum;

    return 0;
}