#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int i,n,v[5000001],p,u,k;
deque <int> dq;
long long S;
int main()
{   f>>n>>k;f>>v[1];
    dq.push_back(1);
    for(i=2;i<=n;i++){
        f>>v[i];
        while(!dq.empty()&&v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i-dq.front()>=k)
            dq.pop_front();
        if(i>=k)
            S=S+v[dq.front()];
    }
    g<<S;
    return 0;
}