#include <fstream>

using namespace std;

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

int dq[5000000],v[5000000],st=0,dr=-1;

int main()
{
    int n,k;
    long long s=0;
    fin>>n>>k;
    for(int i=0; i<n; i++){
        fin>>v[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]];
        }
    }
    fout<<s;
    fin.close();
    fout.close();
    return 0;
}