#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque <int> dq;
int v[5000000];
int main()
{
    int n,k;
    cin>>n>>k;
    long long suma=0;
    for(int i=0;i<n;i++)
    {
        cin>>v[i];
        if(!dq.empty()&&dq.front()==i-k)
        {
            dq.pop_front();
        }
        while(!dq.empty()&&v[i]<=v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);

        if(i>=k-1)
        {
            suma+=v[dq.front()];
        }
    }
    cout<<suma;
    return 0;
}