#include <fstream>
#include <deque>
#include <algorithm>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
int main (void)
{
    int n,k,s=0;
    n-=k;
    in>>n>>k;
    deque<int> a;
    deque<int>::iterator beta;
    for (int i=1;i<=k;++i)
    {
        int l;
        in>>l;
        a.push_back(l);
    }
    beta=min_element(a.begin(),a.end());
    s+=(*beta);
    for (int i=1;i<=n-k;++i)
    {
        int w;
        in>>w;
        a.pop_front();
        a.push_back(w);
        beta=min_element(a.begin(),a.end());
        s+=(*beta);
    }
    out<<s;
    return 0;
}