#include <fstream>
#include <queue>

#define NMAX 5000002

using namespace std;

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

struct element{int val, poz;};

int n, k;
long long int sum;

deque<element> deq;

int main()
{
    int i, x;
    fin>>n>>k;
    for(i = 1; i <= n; i++)
    {
        fin>>x;
        while(!deq.empty() && deq.front().poz <= i - k) //scoate toate elementele dated
        {
            deq.pop_front();
        }
        while(!deq.empty() && deq.back().val > x)
        {
            deq.pop_back();
        }
        deq.push_back({x, i});
        if(i >= k) //am citit macar primele k elemente
          sum += deq.front().val;
    }
    fout<<sum<<'\n';
    return 0;
}