// O(n^2), 30p?
#include <fstream>
#include <vector>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int n, k;
vector <int> v;
int main()
{
    cin>>n>>k;
    for(int i=0;i<n;i++)
    {
        int x;  cin>>x;
        v.push_back(x);
    }
    int MIN=1e7+1, poz=-1;
    for(int i=0;i<k;i++)
        if(v[i]<=MIN)
            MIN=v[i], poz=i;
    long long int sum=MIN;
    for(int i=k;i<n;i++)
    {
        if(poz==i-k)
        {
            MIN=1e7+1;
            for(int j=i-k+1;j<=i;j++)
                if(v[j]<=MIN)
                    MIN=v[j], poz=j;
        }else if(v[i]<=MIN)
                    MIN=v[i], poz=i;
        sum+=MIN;
    }
    cout<<sum;


    return 0;
}