MOD = 10**9+7

N = int(input())
x = list(map(int, input().split()))

ans = 0
mul = 0
for i in range(N-1):
    mul += pow(i+1, MOD-2, MOD)
    ans += (x[i+1] - x[i]) * mul % MOD
    ans %= MOD
for i in range(2, N):
    ans *= i
    ans %= MOD
print(ans)
