#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, k, v[5000001],i;
long long int sum;
deque<int>dq;
int main()
{
    f>>n>>k;
    for(i=0;i<n;i++)
        f>>v[i];
    sum=0;
    for(i=0;i<n;i++)
    {
        if(!dq.empty()&&dq.front()==i-k)
            dq.pop_front();
        while(!dq.empty()&&v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k-1)
        {
            sum=sum+ v[dq.front()];
        }
    }
    g<<sum<<'\n';
    return 0;
}