#include <fstream>
#include <stack>

using namespace std;

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

deque <int> dq;

const int NMAX = 5e6;

int v[NMAX + 1];

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

int main()
{
    int n,k;
    fin >> n >> k;
    fout << deq(n,k);
    return 0;
}