#include <fstream>

using namespace std;
const int NMAX = 5000000;
int v[NMAX], dq[NMAX];
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n, k, st, dr;
    long long s = 0;
    in >> n >> k;
    for(int i= dr = st = 0; i < n; i++)
    {
        in >> v[i];
        if(st <= dr && dq[st] == i - k)
        {
            st++;
        }
        while(st <= dr && v[i] <= v[dq[dr]])
        {
            dr--;
        }
        dq[++dr] = i;
        if(i >= k - 1)
        {
            s += v[dq[st]];
        }
    }
    out << s;
    return 0;
}