#include <fstream>

using namespace std;

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

int dq[5000005];
long long v[50000005];


int main()
{
    int n, k;
    long long suma=0;
    int st, dr = -1;
    in>>n>>k;
    for (int i = 1; i <= n; i++){
        in >> v[i];
        if (st <= dr && dq[st] == i - k)
            st++;
        while (st <= dr && v[i] <= v[dq[dr]])
            dr--;
        dq[++dr] = i;
        if (st <= dr && i >= k)
            suma += v[dq[st]];
    }
    out<<suma;
    return 0;
}