#include <fstream>
#include <deque>
#define NMAX 5000000
using namespace std;
int n, k, v[NMAX+2], dq[NMAX+2], p=1, u;
long long sol;
int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");

    fin>>n>>k;
    for(int i=1; i<=n; i++)
        fin>>v[i];
    for(int i=1; i<=n; i++)
    {
        ///minimul unei secv de lungime k care se termina pe poz i daca aceasta exista

        while(p<=u && v[i]<=v[dq[u]])
            u--;
        dq[++u]=i;

        if(i>=k)///am o subsecventa valida
            sol+=v[dq[p]];
        if(i-dq[p]+1==k)
            p++;

    }
    fout<<sol;


    return 0;
}