#include <fstream>
#include <deque>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
int v[5000007];
deque<int>dq;
int main()
{
    int n,k;
    in>>n>>k;
    int i;
    long long s=0;
    for(i=1;i<=n;i++)
    {
        in>>v[i];
        while(!dq.empty()&&v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front()==i-k)
            dq.pop_front();
        if(i>=k)
            s=s+1LL*v[dq.front()];
    }
    out<<s;
    return 0;
}