#include<bits/stdc++.h>
using namespace std;

typedef long long ll;

// (a^b)%m
ll exp(ll a, ll b, ll m) {
	ll r=1;
	while(b) {
		if(b%2) r=(r*a)%m;
		a=(a*a)%m;
		b/=2;
	}
	return r;
}

// a^-1 %m, prime m
ll invp(ll a, ll m) {
	return exp(a, m-2, m);
}

const int mx=1e5+77;
const int mod=1e9+7;

ll fact[mx];

int main() {
	fact[0]=1;
	for (int i=1; i<mx; i++)
		fact[i]=(fact[i-1]*i)%mod;
	ll inv[mx];
	int N; cin>>N;
	for (int i=1; i<=N-1; i++)
		inv[i]=(fact[N-1]*invp(i,mod))%mod;
	vector<int> x(N+1);
	for (int i=1; i<=N; i++)
		cin>>x[i];
	ll ret=0;
	for (int i=1; i<=N-1; i++)
		ret=(ret+inv[i]*(x[N]-x[i]))%mod;
	cout<<ret<<"\n";
	return 0;
}