#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, k;
int a[5000005], dq[5000005];
long long int s;
int main()
{
    f>>n>>k;
    for(int i=1; i<=n; i++)
        f>>a[i];
    int fr=1, bk=0;
    for(int i=1; i<=n; i++)
    {
        while(a[i]<=a[dq[bk]] && bk>=fr)
            bk--;
        bk++;
        dq[bk]=i;
        if(dq[fr]==i-k)
            fr++;
        if(i>=k)
            s+=a[dq[fr]];
    }
    g<<s;
    return 0;
}