#include<fstream>
#include<deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<int>q;
int v[5000002],i,n,k;
long long s;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++)
    {
        f>>v[i];
        while(!q.empty()&&v[i]<=v[q.back()])
          q.pop_back();
        q.push_back(i);
        if(q.front()<=i-k)
          q.pop_front();
        if(i>=k)
          s+=v[q.front()];
    }
    g<<s;
    return 0;
}