mod = 10**9 + 7
n = int(input())
lx = list(map(int, input().split()))

d = 0
ans = 0

for i in range(1, n):
  f = 1 if i == 1 else f * (i-1) % mod
  d = (d * i + f) % mod
  ans = (ans * i + (lx[i] - lx[i-1]) * d) % mod

print(ans)