#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000009],k,mini=10000009,n,p;
long long s;
int main()
{
    fin>>n>>k;
    s=0;
    for( int j=1;j<=n;j++)
    {
        fin>>v[j];
    }
    for(int j=1;j<=n;j++)
    {
        if(mini>=v[j])
        {
            mini=v[j];
            p=j;
        }
        if(j>=k)
        {
            if(p<j-k+1)
            {
                mini=10000009;
                for(int i=j-k+1;i<=j;i++)
                {
                    if(mini>=v[i])
                    {
                        mini=v[i];
                        p=i;
                    }
                }
            }
            s=s+mini;
        }
    }
    fout<<s;
    fin.close();
    fout.close();
    return 0;
}