#include<fstream>
using namespace std;
long long k, s, a[5000001], i;
int n, p, u, d[5000001];
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>a[i];
    p=u=d[1]=1;
    for(i=2;i<=n;i++)
    {
        while(a[i]<a[d[u]]&&p<=u)
            u--;
        d[++u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            s+=a[d[p]];
    }
    g<<s;
    return 0;
}