#include <bits/stdc++.h>
#include<algorithm>
#include<vector>
#include<string>
#include<cmath>
#include <unordered_set>
#include<deque>
using namespace std;

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

deque<int> dq;
vector<int> v;

int main()

{
    int n,k,x;
    long long sum=0;

    f>>n>>k;

    for(int i=1; i<=n; i++)
    {
        f>>x;
        v.push_back(x);
    }

    dq.push_back(0);

    for(int i=1; i<n; i++)
    {
        while(!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();

        dq.push_back(i);
        if(dq.front() == i-k)
            dq.pop_front();
        if(i >= k-1)
        {
            sum += v[dq.front()];
            //cout<<v[dq.front()]<<endl;
        }


    }

    g<<sum;





    return 0;


}