#include <iostream>
#include <fstream>
using namespace std;
int t[5000001],v[5000001];
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int N,K,i,suma=0,a=0,b=-1;
    fin>>N>>K;
    for(i=0;i<=N-1;i++)
    {
        fin>>v[i];
        if(a<=b && t[a]==i-K)
        {
            a++;
        }
        while(a<=b && v[i]<=v[t[b]])
        {
            b--;
        }
        t[++b]=i;
        if(i>=K-1)
        {
            suma=suma+v[t[a]];
        }
    }
    fout<<suma;
    fin.close();
    fout.close();
    return 0;
}