#include <fstream>
using namespace std;
ifstream F ("deque.in");
ofstream G ("deque.out");
int dq[5000001], x, n, k, bk = 0, fr = 1, v[5000001];
long long sum = 0;
int main()
{
    F>>n>>k;
    for(int i = 1; i <= n; i++)
        F>>v[i];

    for(int i = 1; i <= n; i++)
    {
        while (v[i] <= v[dq[bk]]  && fr <= bk)
            bk--;

        bk++;
        dq[bk] = i;

        if (dq[fr] == i - k)
            fr++;

        if(i >= k)
            sum += v[dq[fr]];

    }
    G<<sum;
    return 0;
}