#include <iostream>
#include <fstream>
#include <stack>
using namespace std;

deque<int> deq;
ifstream f("deque.in");
ofstream g("deque.out");
int v[10000001],k;
long long suma;
int main()
{   int n;
    f>>n>>k;
    for (int i=0; i<n; i++)
    {
        f>>v[i];
        if (!deq.empty() && deq.front()==i-k)
        {
            deq.pop_front();
        }
        while (!deq.empty() && v[i]<=v[deq.back()])
        {
            deq.pop_back();
        }
        deq.push_back(i);
        if (i>=k-1)
        {
            suma= suma + v[deq.front()];
        }
    }
g<<suma;
f.close();
g.close();
return 0;
}