#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

deque <int> a,b;
int mini=100000004;
int n,k,cnt,i,s,nr;
int main()
{
    fin>>n>>k;
    for(int i=1; i<=n; i++)
    {
        fin>>nr;
        mini=min(mini,nr);
            a.push_back(nr);
            b.push_back(nr);
        if(i==k){
            s+=mini;
        }
        else if(i>k){
            if(a.front()!=mini){
                a.pop_front();
            }
            else{
                mini=100000004;
                b.pop_front();
                while(!b.empty()){
                    int x=b.front();
                    mini=min(mini,x);
                    b.pop_front();
                }
                a.pop_front();
            }
            s+=mini;
        }
    }
    fout<<s;
    return 0;
}