#include<fstream>
#include<queue>
using namespace std;

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

deque<int> q;

int n,k,v[5000005];

int main()
{
    fin>>n>>k;

    for(int i=1;i<=n;i++)
        fin>>v[i];

    long long sum=0;

    for(int i=1;i<=n;i++) //capatul din dreapta al secventei pentru care vrem sa aflam minimul
    {
        if(i>=k)
        {
           if(!q.empty() && q.front()==i-k) q.pop_front();
           while(!q.empty() && v[q.back()]>=v[i]) q.pop_back();
           q.push_back(i);
           sum+=1LL*v[q.front()];
        }
        if(!q.empty() && q.front()==i-k) q.pop_front();
        while(!q.empty() && v[q.back()]>=v[i]) q.pop_back();
        q.push_back(i);
    }

    fout<<sum<<'\n';
    return 0;
}