#include <fstream>
#include <deque>
using namespace std;
int v[5000001];
deque<int>d;
ifstream in("deque.in");
ofstream out("deque.out");
int main()
{
    int n,k;
    long long s=0;
    in>>n>>k;
    for(int i=0;i<n;i++){
        in>>v[i];
        if(d.front()==i-k)
            d.pop_front();
        while(!d.empty() && v[i]<=v[d.back()])
            d.pop_back();
        d.push_back(i);
        if(i>=k-1)
            s+=v[d.front()];
    }
    out<<s;
    return 0;
}