import math

n = int(input())
x = list(map(int, input().split()))
ans = 0
mod = 10 ** 9 + 7
v = math.factorial(n - 1)


for i in range(1, n):
    w = (v//i)%mod
    ans += ((x[n - 1] - x[i - 1]) * w)%mod


print(int(ans))