#include <fstream>


#define nMax  5000001
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, v[nMax], deque[nMax];
long long Sol;
int main()
{
    fin>>n>>k;
    int st=1, dr=0;
    for(int i=1; i<=n; i++)
    {
        fin>>v[i];
        while(v[i]<=v[deque[dr]] && st<=dr)
            dr--;
        deque[++dr]=i;

        while(i-k>=deque[st])
            st++;

        if(i>=k)
            Sol+=v[deque[st]];
    }
    fout<<Sol;
}