N = int(input())
X = list(map(int,input().split()))
S = []
dp = [1]
mod = 10**9+7
for i in range(N):
    t = i+1
    dp.append(dp[i]*t)
ans = 0
for i in range(N-1):
    x = X[i]
    S.append(X[N-1]-x)
ans = 0
for i in range(N-1):
    x = S[i]
    t = i + 1
    ans += dp[N-1]//t*x%mod
print(ans%mod)