n = int(input())
l = list(map(int,input().split()))
sa = []
for i in range(n-1):
    sa.append(l[i+1]-l[i])

mod = 10**9+7
ans = 0
count = 0
kai = 1
for i in range(n-1):
    count += 1/(i+1)
    kai *= (i+1)
    kai %= mod
    ans += sa[i]*count
    ans %= mod

print(int(kai*ans%mod))
