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

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    int n, k, v[100001], min, suma=0, i, j;
    f>>n>>k;

    for(i=0;i<n;i++)
      f>>v[i];

    j=0;
    for(i=k-1;i<n;i++){
        min=v[i-k+1];
        for(j=i-k+1;j<=i;j++){
          if(v[j]<min){
            min=v[j];
          }
        }
        suma+=min;
    }
    g<<suma;
    return 0;
}