#include <fstream>

using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int n, k, i, p, u, v[5000001], d[5000001];
long long sol;
int main()
{
    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;
}