#include <fstream>
using namespace std;
int n, k, i, p, u, v[5000001], d[5000001];
long long sol;
ifstream fin ("deque.in");
ofstream fout ("deque.out");

int main () {
    fin>>n>>k;
    for (i=1;i<=n;i++) {
        fin>>v[i];
    }

    p=1; u=1; d[u]=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;
}