#include <fstream>
#include <deque>
#define DIM 5000001

using namespace std;

int v[DIM];
deque<int> d;
int n, p, u, i, k;
long long suma = 0;

int main () {

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

    for (i=1;i<=n;i++) fin>>v[i];
    d.push_back(1);
    if (k == 1)suma = v[1];

    for (i=2;i<=n;i++) {

        while (!d.empty() && v[i] <= v[d.back()])
            d.pop_back();
        d.push_back(i);
        if (i - d.front() == k)
            d.pop_front();

        if (i >= k) {
            suma += v[ d.front() ];
        }
    }
    fout<<suma;

    return 0;
    }