#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
#define NMAX 5000000
#define VALMAX 10000000
int n,x[NMAX+1],dq[NMAX+1],k,f,b;
long long s;
int main()
{
    fin >> n >> k;
    for (int i=1; i<=n; i++)
        fin >> x[i];
    f=1;
    b=0;
    for (int i=1; i<=n; i++)
    {
        while (f<=b && x[i]<=x[dq[b]])
            b--;
        b++;
        dq[b]=i;
        if (dq[f]==i-k)
            f++;
        if (i>=k)
            s+=x[dq[f]];
    }
    fout << s;
    return 0;
}