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

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

vector<int> v;
deque<int> q;

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