#include <deque>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque <int> dq;
int a[5000000];
int main()
{
    int n, k;
    in>>n>>k;
    long long s=0;
    for(int i=0;i<n;i++)
    {
        in>>a[i];
        if(!dq.empty()&&dq.front()==i-k)
            dq.pop_front();
        while(!dq.empty()&&a[i]<=a[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k-1)
            s+=a[dq.front()];
    }
    out<<s;
    return 0;
}