#include <fstream>
using namespace std;
int v[5000000];
ifstream fin("deque.in");
ofstream fout("deque.out");
int main()
{
   int n,k,p;
   long long s=0,minim;
   fin>>n>>k;
   for(int i=1;i<=n;i++)
        fin>>v[i];
   for(int i=1;i<=n-k+1;i++)
   {
       p=1;
       minim=v[i];
       while( p<k)
       {
           if(v[i+p]<minim)
                minim=v[i+p];
           p++;
       }
       if(p==k)
        s=s+minim;
   }
   fout<<s;
    return 0;
}