Do you know "sed," a tool provided with Unix? Its most popular use is to substitute every occurrence of a string  contained in the input string (actually each input line) with another string β. More precisely, it proceeds as follows.

1. Within the input string, every non-overlapping (but possibly adjacent) occurrences of α are marked. If there is more than one possibility for non-overlapping matching, the leftmost one is chosen.
2. Each of the marked occurrences is substituted with β to obtain the output string; other parts of the input string remain intact.



For example, when α is "aa" and β is "bca", an input string "aaxaaa" will produce "bcaxbcaa", but not "aaxbcaa" nor "bcaxabca". Further application of the same substitution to the string "bcaxbcaa" will result in "bcaxbcbca", but this is another substitution, which is counted as the second one.

In this problem, a set of substitution pairs (αi, βi) (i = 1, 2, ... , n), an initial string γ, and a final string δ are given, and you must investigate how to produce δ from γ with a minimum number of substitutions. A single substitution (αi, βi) here means simultaneously substituting all the non-overlapping occurrences of αi, in the sense described above, with βi.

You may use a specific substitution (αi, βi ) multiple times, including zero times.



Input

The input consists of multiple datasets, each in the following format.

n
α1 β1
α2 β2
.
.
.
αn βn
γ δ

n is a positive integer indicating the number of pairs. αi and βi are separated by a single space. You may assume that 1 ≤ |αi| < |βi| ≤ 10 for any i (|s| means the length of the string s), αi ≠ αj for any i ≠ j, n ≤ 10 and 1 ≤ |γ| < |δ| ≤ 10. All the strings consist solely of lowercase letters. The end of the input is indicated by a line containing a single zero.

Output

For each dataset, output the minimum number of substitutions to obtain δ from γ. If δ cannot be produced from γ with the given set of substitutions, output -1.

Example

Input

2
a bb
b aa
a
bbbbbbbb
1
a aa
a
aaaaa
3
ab aab
abc aadc
ad dee
abc
deeeeeeeec
10
a abc
b bai
c acf
d bed
e abh
f fag
g abe
h bag
i aaj
j bbb
a
abacfaabe
0


Output

3
-1
7
4
#include<bits/stdc++.h>

using namespace std;
#define INFS (1LL<<28)
#define DEKAI 1000000007
#define INF 1000000007
//#define MOD 1000000007
#define lp(i,n) for(int i=0;i<n;i++)
#define lps(i,n) for(int i=1;i<=n;i++)
#define all(c) begin(c), end(c)

//#define int long long 

namespace {
	#define __DECLARE__(C)    \
	    template <typename T> \
	std::ostream &operator<<(std::ostream &, const C<T> &);

	#define __DECLAREM__(C)               \
	    template <typename T, typename U> \
	std::ostream &operator<<(std::ostream &, const C<T, U> &);

	__DECLARE__(std::vector)
	__DECLARE__(std::deque)
	__DECLARE__(std::set)
	__DECLARE__(std::stack)
	__DECLARE__(std::queue)
	__DECLARE__(std::priority_queue)
	__DECLARE__(std::unordered_set)
	__DECLAREM__(std::map)
	__DECLAREM__(std::unordered_map)

	template <typename T, typename U>
	std::ostream &operator<<(std::ostream &, const std::pair<T, U> &);
	template <typename... T>
	std::ostream &operator<<(std::ostream &, const std::tuple<T...> &);
	template <typename T, std::size_t N>
	std::ostream &operator<<(std::ostream &, const std::array<T, N> &);

	template <typename Tuple, std::size_t N>
	struct __TuplePrinter__ {
		static void print(std::ostream &os, const Tuple &t) {
			__TuplePrinter__<Tuple, N - 1>::print(os, t);
			os << ", " << std::get<N - 1>(t);
		}
	};

	template <typename Tuple>
	struct __TuplePrinter__<Tuple, 1> {
		static void print(std::ostream &os, const Tuple &t) { os << std::get<0>(t); }
	};

	template <typename... T>
	std::ostream &operator<<(std::ostream &os, const std::tuple<T...> &t) {
		os << '(';
		__TuplePrinter__<decltype(t), sizeof...(T)>::print(os, t);
		os << ')';
		return os;
	}

	template <typename T, typename U>
	std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &v) {
		return os << '(' << v.first << ", " << v.second << ')';
	}

	#define __INNER__                             \
	os << '[';                                \
	for (auto it = begin(c); it != end(c);) { \
		os << *it;                            \
		os << (++it != end(c) ? ", " : "");   \
	}                                         \
	return os << ']';

	template <typename T, std::size_t N>
	std::ostream &operator<<(std::ostream &os, const std::array<T, N> &c) {
		__INNER__
	}

	#define __DEFINE__(C)                                           \
	    template <typename T>                                       \
	std::ostream &operator<<(std::ostream &os, const C<T> &c) { \
		__INNER__                                               \
	}

	#define __DEFINEM__(C)                                             \
	    template <typename T, typename U>                              \
	std::ostream &operator<<(std::ostream &os, const C<T, U> &c) { \
		__INNER__                                                  \
	}

	#define __DEFINEW__(C, M1, M2)                                  \
	    template <typename T>                                       \
	std::ostream &operator<<(std::ostream &os, const C<T> &c) { \
		std::deque<T> v;                                        \
		for (auto d = c; !d.empty(); d.pop()) v.M1(d.M2());     \
			return os << v;                                         \
	}

	__DEFINE__(std::vector)
	__DEFINE__(std::deque)
	__DEFINE__(std::set)
	__DEFINEW__(std::stack, push_front, top)
	__DEFINEW__(std::queue, push_back, front)
	__DEFINEW__(std::priority_queue, push_front, top)
	__DEFINE__(std::unordered_set)
	__DEFINEM__(std::map)
	__DEFINEM__(std::unordered_map)
}

#define pii pair<int,int>
#define ll long long
inline ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

// modint 
template <signed M, unsigned T>
struct mod_int {
	constexpr static signed MODULO = M;
	constexpr static unsigned TABLE_SIZE = T;

	signed x;

	mod_int() : x(0) {}

	mod_int(long long y) : x(static_cast<signed>(y >= 0 ? y % MODULO : MODULO - (-y) % MODULO)) {}

	mod_int(int y) : x(y >= 0 ? y % MODULO : MODULO - (-y) % MODULO) {}

	mod_int &operator+=(const mod_int &rhs) {
		if ((x += rhs.x) >= MODULO) x -= MODULO;
		return *this;
	}

	mod_int &operator-=(const mod_int &rhs) {
		if ((x += MODULO - rhs.x) >= MODULO) x -= MODULO;
		return *this;
	}

	mod_int &operator*=(const mod_int &rhs) {
		x = static_cast<signed>(1LL * x * rhs.x % MODULO);
		return *this;
	}

	mod_int &operator/=(const mod_int &rhs) {
		x = static_cast<signed>((1LL * x * rhs.inv().x) % MODULO);
		return *this;
	}

	mod_int operator-() const { return mod_int(-x); }

	mod_int operator+(const mod_int &rhs) const { return mod_int(*this) += rhs; }

	mod_int operator-(const mod_int &rhs) const { return mod_int(*this) -= rhs; }

	mod_int operator*(const mod_int &rhs) const { return mod_int(*this) *= rhs; }

	mod_int operator/(const mod_int &rhs) const { return mod_int(*this) /= rhs; }

	bool operator<(const mod_int &rhs) const { return x < rhs.x; }

	mod_int inv() const {
		assert(x != 0);
		if (x <= static_cast<signed>(TABLE_SIZE)) {
			if (_inv[1].x == 0) prepare();
			return _inv[x];
		} else {
			signed a = x, b = MODULO, u = 1, v = 0, t;
			while (b) {
				t = a / b;
				a -= t * b;
				std::swap(a, b);
				u -= t * v;
				std::swap(u, v);
			}
			return mod_int(u);
		}
	}

	mod_int pow(long long t) const {
		assert(!(x == 0 && t == 0));
		mod_int e = *this, res = mod_int(1);
		for (; t; e *= e, t >>= 1)
			if (t & 1) res *= e;
		return res;
	}

	mod_int fact() {
		if (_fact[0].x == 0) prepare();
		return _fact[x];
	}

	mod_int inv_fact() {
		if (_fact[0].x == 0) prepare();
		return _inv_fact[x];
	}

	mod_int choose(mod_int y) {
		assert(y.x <= x);
		return this->fact() * y.inv_fact() * mod_int(x - y.x).inv_fact();
	}

	static mod_int _inv[TABLE_SIZE + 1];

	static mod_int _fact[TABLE_SIZE + 1];

	static mod_int _inv_fact[TABLE_SIZE + 1];

	static void prepare() {
		_inv[1] = 1;
		for (int i = 2; i <= (int)TABLE_SIZE; ++i) {
			_inv[i] = 1LL * _inv[MODULO % i].x * (MODULO - MODULO / i) % MODULO;
		}
		_fact[0] = 1;
		for (unsigned i = 1; i <= TABLE_SIZE; ++i) {
			_fact[i] = _fact[i - 1] * int(i);
		}
		_inv_fact[TABLE_SIZE] = _fact[TABLE_SIZE].inv();
		for (int i = (int)TABLE_SIZE - 1; i >= 0; --i) {
			_inv_fact[i] = _inv_fact[i + 1] * (i + 1);
		}
	}
};

template <int M, unsigned F>
std::ostream &operator<<(std::ostream &os, const mod_int<M, F> &rhs) {
	return os << rhs.x;
}

template <int M, unsigned F>
std::istream &operator>>(std::istream &is, mod_int<M, F> &rhs) {
	long long s;
	is >> s;
	rhs = mod_int<M, F>(s);
	return is;
}

template <int M, unsigned F>
mod_int<M, F> mod_int<M, F>::_inv[TABLE_SIZE + 1];

template <int M, unsigned F>
mod_int<M, F> mod_int<M, F>::_fact[TABLE_SIZE + 1];

template <int M, unsigned F>
mod_int<M, F> mod_int<M, F>::_inv_fact[TABLE_SIZE + 1];

template <int M, unsigned F>
bool operator==(const mod_int<M, F> &lhs, const mod_int<M, F> &rhs) {
	return lhs.x == rhs.x;
}

template <int M, unsigned F>
bool operator!=(const mod_int<M, F> &lhs, const mod_int<M, F> &rhs) {
	return !(lhs == rhs);
}

const int MF = 1000010;
const int MOD = 1000000007;

using mint = mod_int<MOD, MF>;

mint binom(int n, int r) { return (r < 0 || r > n || n < 0) ? 0 : mint(n).choose(r); }

mint fact(int n) { return mint(n).fact(); }

mint inv_fact(int n) { return mint(n).inv_fact(); }
const ll mod = 1000000007;
const int MAX_N = 10000;  // 400MB
// const int MAX_N = 1024; // 4MB
// nCr % mod

#define int long long
#define double long double 

inline ll gcds(ll a, ll b) { return b ? gcds(b, a % b) : a; }

#define RK 200000000000
#define LK 300000000000
#define PL 400000000000
#define MI 500000000000
#define KA 600000000000
string target;
vector<pair<string,string>> v;
int ans;

void sed(string &ss,string b,string to){
	//cout<<"!"<<ss<<" "<<b<<" "<<to<<endl;
	string s=ss;
	if(s.size()<b.size())return;
	lp(i,500){
		if(i>=s.size()-b.size()+1){
			//cout<<"!!!"<<s<<" "<<b<<" "<<i<<endl;
			break;
		}
		if(s.substr(i,b.size())==b){
			string bef=s.substr(0,i);
			string af=s.substr(i+b.size(),s.size()-i-b.size());
			//cout<<" "<<bef<<" "<<af<<" "<<bef+to+af<<" "<<bef.size()+to.size()<<endl;
			s=bef+to+af;
			i=bef.size()+to.size()-1;
		}
	}
	ss=s;
}

void solve(string s,int x){
	if(s.size()>target.size())return;
	if(s==target){
		ans=min(x,ans);
		return;
	}
	if(x>ans)return;
	lp(z,v.size()){
		string t=v[z].first,to=v[z].second;
		string b=s;
		sed(b,t,to);
		if(b!=s){
			solve(b,x+1);
		}
	}
}

signed main(){
	while(1){
		int n;
		cin>>n;
		if(n==0)break;
		v.clear();
		lp(i,n){
			string s,t;
			cin>>s>>t;
			v.push_back({s,t});
		}
		string s;
		cin>>s>>target;
		ans=20;
		solve(s,0);
		if(ans==20)ans=-1;
		cout<<ans<<endl;
	}
	return 0;
}
