#include <fstream>
#include <deque>

using namespace std;

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

int n, i, k, p, u;
int v[5000005], d[5000005];

long long sum;

int main()
{
    fin >> n >> k;
    for (i=1; i<=n; i++){
        fin >> v[i];
    }
    p = u = 1, d[1] = 1;
    for (i=2; i<=n; i++){
        while (v[i] <= v[d[u]] && p <= u){
            u--;
        }
        d[++u] = i;
        if (i - d[p] == k){
            p++;
        }
        if (i >= k){
            sum += v[d[p]];
        }
    }
    fout << sum;
    return 0;
}