#include <fstream>
#include <deque>
using namespace std;
deque<int> dq;
ifstream cin("deque.in");
ofstream cout("deque.out");
int v[5000001];
int main()
{
    long long n,i,j,s=0,k;
    cin>>n>>k;

    for(i=1;i<=n;i++)
    {
        cin>>v[i];
    }
    for(i=1;i<=k;i++)
    {
        while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
    }
    for(i=k+1;i<=n;i++)
    {
        s+=1LL*v[dq.front()];
        //right = i, left = i - k + 1
        if(dq.front()==i-k)
            dq.pop_front();
         while(!dq.empty() && v[dq.back()]>v[i])
            dq.pop_back();
        dq.push_back(i);
    }
    s+=1LL*v[dq.front()];
    cout<<s;
    return 0;
}