#include <fstream>
#include <list>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
list <int> l;
int v[5000005];
int main()
{
    long long n,k,a,sum=0;
    cin>>n>>k;
    for(long long i=1; i<=n; i++)
    {
        cin>>a;
        v[i]=a;
        while(l.empty()==0&&a<=v[l.back()])
            l.pop_back();
        l.push_back(i);
        if(l.front()==i-k)
            l.pop_front();
        if(i>=k)
            sum+=v[l.front()];
    }
    cout<<sum;
    return 0;
}