def main1(n,k,a):
  if k==1:return max(a)-min(a)
  a.sort()
  ary=[]
  for i,(x,y) in enumerate(zip(a,a[1:])):
    ary.append(y-x)
  ary.sort()
  return max(a)-min(a)-sum(ary[-k+1:])

if __name__=='__main__':
  n,k=map(int,input().split())
  a=list(map(int,input().split()))
  #ret0=main0(n,k,a)
  ret1=main1(n,k,a)
  #print(ret0)
  print(ret1)