N, M = map(int, input().split(' '))
d = [int(input()) for i in range(M)]
k = 0
ans = 0
for i in range(N):
    idx = None
    t = 10 ** 6
    for i, td in enumerate(d):
        if t > abs(k - td):
            t = abs(k - td)
            idx = i
    k = d[idx]
    d.pop(idx)
    ans += t
print(ans)