import math
N = int(input())
xn = list(map(int, input().split()))

if N > 2000:
    exit()
ans = 0
for i in range(N-1):
    for j in range(N-1-i):
        ans += (xn[i+1+j]-xn[i])/(N-1-j)
    for l in range(j):
        ans += (xn[i]-xn[i-j]/(N-1-l))
print(int(ans*math.factorial(N-1)))