#include <fstream>

using namespace std;

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

int v[5000002],dq[5000002],n,k;
long long s;

int main()
{
    in>>n>>k;
    int st=0,dr=-1;
    for(int i=0;i<n;i++){
        in>>v[i];
        //dq[i]=i;
        if(st<=dr && dq[st]==i-k){
            st++;
        }
        while (st<=dr && v[i]<=v[dq[dr]]){
            dr--;
        }
        dq[++dr]=i;
        if(i>=k-1)
            s+=v[dq[st]];
    }
    out<<s;
    return 0;
}