#include <fstream>
#include <deque>

using namespace std;

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

const int Nmax = 5000005;
int v[Nmax];
deque<int> dq;

int main()
{
    int N,K,i;
    long long sum;
    fin >> N >> K;
    sum = 0;
    for(i=1;i<=N;i++){
        fin >> v[i];
        while(!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=K){
            if(dq.front()<=i-K)
                dq.pop_front();
            sum+=(long long)v[dq.front()];
        }
    }
    fout << sum;
    return 0;
}