const int N = 2000 * 1000 + 3000;

int n;
int a[N];

inline bool read() {
  n = nextInt();
  forn(i, n) {
   	a[i] = nextInt();
  }
	return true;

}

int cnt[N];
int curVal;

inline int getsum(int l, int r) {
	if (l > r) return 0;

 	if (r >= N) {
 		r = N - 1;
 	}

 	int res = cnt[r];

 	if (l > 0) res -= cnt[l - 1];
 	return res;
}

inline bool f(int mid) {
 	for(int i = curVal; i < N / 2; i += curVal) {
		int curpos = i + mid;
		if (getsum(curpos, i + curVal - 1) > 0)
			return true;
 	}

 	return false;
}

inline void solve() {
	forn(i, n) {
	 	cnt[a[i]] ++;
	}
	forn(i, N) {
	 	if (i > 0) {
	 	 	cnt[i] += cnt[i - 1];
	 	}
	}

	sort(a, a + n);
	n = int(unique(a, a + n) - a);

	int ans = 0;


	forn(i, n) {
	 	curVal = a[i];

	 	int l = 0;
	 	int r = a[i];

  	while (r - l > 1) {
  	 	int mid = (r + l) >> 1;

  	 	if (f(mid)) {
  	 		l = mid;
  	 	} else {
  	 	 	r = mid;
  	 	}
  	}

  	ans = max(ans, l);
  }

  cout << ans << endl;
}

int main()
{

#ifdef gridnevvvit
	freopen("input.txt", "rt", stdin);
	freopen("output.txt", "wt", stdout);
#endif

	//srand(time(NULL));

	cout << setprecision(10) << fixed;
	cerr << setprecision(5) << fixed;

	assert(read());
	solve();

#ifdef gridnevvvit
	cerr << "===Time: " << clock()  << "===" << endl;
#endif

}