#include <stdio.h>
int main(int argc, char const *argv[]) {

  int num_baggages; // ???????????°
  int num_trucks;   // ?????????????????°
  int p;            // ?????????
  int i;
  int sum_w;        // ???????????????????????§????????????????????????????¨?
  int count_trucks;

  scanf("%d %d",&num_baggages,&num_trucks);
  int baggages[num_baggages]; // ??????????????????

  for( i = 0 ; i < num_baggages ; i++ ){
    scanf("%d",&baggages[i]);
    p += baggages[i];
  }

  // ?????????????????????????????????????????????
  p /= num_trucks+1;

  

    

  printf("%d\n",p);

  return 0;
}