#include <bits/stdc++.h>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int main() {

long long n,k;
deque <long long> dq;

in>>n>>k;
long long sum=0;
vector <int> v(n+1);

for(int i=0;i<n;i++)
{

    in>>v[i];

    if(!dq.empty() && dq.front()+k==i)
    {
        dq.pop_front();
    }
    while(!dq.empty() && v[i]<=v[dq.back()])
    {
        dq.pop_back();
    }


    dq.push_back(i);
    if (i >= k - 1)
        {
            sum += v[dq.front()];
        }

}
out<<sum;

    return 0;
}