N, K = map(int, input().split())
A = sorted(list(map(int, input().split())))
D = [0 for _ in range(N - 1)]
for i in range(N - 1):
	D[i] = A[i + 1] - A[i]
D.sort()
print(sum(D[:-K + 1]) if not K == 1 else sum(D))