#include <fstream>
#include <deque>

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