#coding: utf-8

def main():
  n,k = map(int, input().split(' '))
  an = list(map(int, input().split(' ')))
  an = sorted(an)
  diff_list = diff(an)
  refine_list = diff_list[:len(diff_list)-(k-1)]
  print(sum(refine_list))


def diff(an):
  diff_list = [an[i] - an[i-1] for i in range(1,len(an))]
  return sorted(diff_list)


if __name__ == '__main__':
  main()