#include <fstream>
#include <deque> 
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
    int n,k;
    fin>>n>>k;
    
    int* a = new int[n + 1];
    deque<int> dq;
    long long suma = 0;

    for(int i = 1;i<=n;i++)
    {
        fin>>a[i];

        while(!dq.empty() && a[dq.back()] >= a[i])
            dq.pop_back();
        
        dq.push_back(i);

        while(!dq.empty() && dq.front() <= i - k)
            dq.pop_front();

        if(i>=k)
            suma+=a[dq.front()];
    }

    fout<<suma;

    delete[] a;
    return 0;

}