#include<iostream>
#include<fstream>
#include<deque>
#include<vector>
using namespace std;

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

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