#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int NMAX=5000005;
int a[NMAX];
deque<int> D;
int main()
{
    int n,k;
    f>>n>>k;
    long long s=0;
    for(int i=1;i<=n;i++)
        f>>a[i];
    for(int i=1;i<=n;i++)
    {
        while(!D.empty() && a[i]<=a[D.back()])
            D.pop_back();
        D.push_back(i);
        while(D.front()<=i-k)
            D.pop_front();
        if(i>=k)
            s+=a[D.front()];
    }
    g<<s<<"\n";
    return 0;
}