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