//Deresu Roberto - FMI
//Re :)
#include<fstream>
#include<deque>
#define nx 5000007
using namespace std;
int n,k,a[nx];
long long s;
deque<int>q;

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

int main()
{
    fin>>n>>k;

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

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

        if(q.front() <= i-k) q.pop_front();

        if(i >= k) s += a[q.front()];
    }

    fout<<s;

    return 0;
}