#include <fstream>
using namespace std;
int V[5000001], D[5000001], u, i, p, n, k;
long long sol;

int main () {
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    fin>>n>>k;
    for (i=1;i<=n;i++)
        fin>>V[i];
    p=1, u=1, D[1]=1;
    for (i=2;i<=n;i++) {
        while (V[i] < V[ D[u] ] && p<=u)
            u--;
        u++;
        D[u]=i;
        if (i-D[p] == k)
            p++;
        if (i>=k)
            sol+= V[ D[p] ];
    }

    fout<<sol;
    return 0;
}