n, k = [ int(v) for v in input().split() ]
natural_number_list = sorted([ int(v) for v in input().split() ])

difference_list = sorted([ (natural_number_list[i+1] - natural_number_list[i])  for i in range(len(natural_number_list)-1) ], reverse = True)

for i in range(k-1):
	difference_list[i] = 0

print(sum(difference_list))