#include <fstream>
#include <deque>
#include <algorithm>

using namespace std;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    unsigned int n, k, i;
    long long suma = 0;
    deque<long long> a;
    fin >> n >> k;
    a.resize(k);
    for(i = 0; i < k; i++)
    {
        fin >> a[i];
    }
    for(i = 2; i < n; i++)
    {
        suma += *min_element(a.begin(), a.end());
        a.pop_front();
        a.push_back(0);
        fin >> a.back();
    }
    fout << suma;
    return 0;
}