#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int n,k,v[5000002];
long long s;
deque<int>q;
int main()
{
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        cin>>v[i];
        if(i>k)
            s+=v[q.front()];
        while(!q.empty()&&i-q.front()>=k)
            q.pop_front();
        while(!q.empty()&&v[i]<=v[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    s+=v[q.front()];
    cout<<s;
    return 0;
}