#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,i,k,auxk,v[5000001],minim,S,a;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    for(i=1;i<=n-(k-1);i++)
    {
        auxk=k;minim=10000000;a=0;
        while(auxk)
        {
            if(v[i+a]<minim)
                minim=v[i+a];
            auxk--;a++;
        }
        S=S+minim;
    }
    fout<<S;
    return 0;
}