#include <fstream>
#include <deque>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");

int n, k, v[5000001], i;
long long s;
deque<int> d;

int main()
{
    cin>>n>>k;
    for(i=1; i<=n; i++)
    {
        cin>>v[i];
        while(d.empty()==0 && v[i]<=v[d.back()]) d.pop_back();
        d.push_back(i);
        if(d.front()==i-k) d.pop_front();
        if(i>=k) s+=v[d.front()];
    }
    cout<<s;
    return 0;
}