#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

deque<int> dq;
int v[5000001];

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