#include <iostream>
#include <fstream>

#define inf 9999999

using namespace std;

      ifstream fin("deque.in");
      ofstream fout("deque.out");

int a[10000];
int min[10000];

int main()
{
    int i,j,n,m,k,mi=inf,s=0;
    fin>>n>>k;
    for(i=1;i<=n;i++)
    fin>>a[i];
    for(i=1;i<=n-k+1;i++)
    {
            for(j=1;j<=k;j++)
            {
            if(mi>a[i+j-1])mi=a[i+j-1];
            }
    s+=mi;
    mi=inf;
    }
    fout<<s;
}