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

using namespace std;

int v[5000001];

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

    int n, k;
    fin >> n >> k;

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

    fout << s;

    return 0;
}