#include <fstream>
#include <deque>
using namespace std;
deque<pair<int, int> >q;
ifstream cin("deque.in");
ofstream cout("deque.out");
int main()
{
    long long ans=0;
    int n,x,k;
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        cin>>x;
        while(!q.empty() && q.back().second>=x)
        {
            q.pop_back();
        }
        q.push_back({i,x});
        if(q.front().first==i-k)
        {
            q.pop_front();
        }
        if(i>=k)
        {
            ans=ans+q.front().second;
        }
    }
    cout<<ans;

    return 0;
}