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

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

int n, k, sum;
vector <int> v;
deque <int> dq;

int main()
{
    f >> n >> k;
    v = vector <int> (n + 1);
    for(int i = 1; i <= n; ++i)
        f >> v[i];
    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 + 1)
            dq.pop_front();
        if(i >= k)
            sum += v[dq.front()];
    }
    g << sum;
}