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

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n, k, x, mn = 999999999;
    long long sum = 0;
    fin >> n >> k;
    deque<int> d;
    for(int i = 1; i <= n; i++) {
        fin >> x;
        d.push_back(x);
        if(d.size() == k) {
            mn = 999999999;
            for(auto j : d) {
                mn = min(mn, j);
            }
            d.pop_front();
            sum += mn;
        }
    }
    fout << sum;
    return 0;
}