#include <iostream>
#include <fstream>
using namespace std;

    const int z=5000001;
    int v[z],n,k,m;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    long long s=0,i,j,x=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];
    while (x<=n-k)
    {
        m=v[x+1];
            for(j=1+x;j<=k+x;j++)
            {
                if (v[j]<m)
                {
                    m=v[j];
                }

            }
        x++;
        s=s+m;

}
g<<s;
return 0;
}