import math
N, M = map(int,raw_input().split())
Dm = []
count = 0
position = 0
cost = 0



for i in range(M):
	Dm.append(input())

while count < N:
	for i in range(len(Dm)):
		if i == 0:
			dif = math.fabs(position - Dm[i])
			temp1 = Dm[i]
			temp2 = i

		else:
			if(dif > math.fabs(position - Dm[i])):
				dif = math.fabs(position - Dm[i])
				temp1 = Dm[i]
				temp2 = i

	del Dm[temp2]
	cost += dif
	position = temp1
	count += 1

print int(cost)