#include "bits/stdc++.h"

#define REP(i,n) for(ll i=0;i<n;++i)
#define RREP(i,n) for(ll i=n-1;i>=0;--i)
#define FOR(i,m,n) for(ll i=m;i<n;++i)
#define RFOR(i,m,n) for(ll i=n-1;i>=m;--i)
#define ALL(v) (v).begin(),(v).end()
#define PB(a) push_back(a)
#define UNIQUE(v) v.erase(unique(ALL(v)),v.end());
#define DUMP(v) REP(aa, (v).size()) { cout << v[aa]; if (aa != v.size() - 1)cout << " "; else cout << endl; }
#define INF 1000000001ll
#define MOD 1000000007ll
#define EPS 1e-9

const int dx[8] = { 1,1,0,-1,-1,-1,0,1 };
const int dy[8] = { 0,1,1,1,0,-1,-1,-1 };


using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
ll max(ll a, int b) { return max(a, ll(b)); }
ll max(int a, ll b) { return max(ll(a), b); }
ll min(ll a, int b) { return min(a, ll(b)); }
ll min(int a, ll b) { return min(ll(a), b); }
///(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)(?´????????`)///
int n;
string y, z;
int dfs(string s, vector<string> &a, vector<string> &b) {
	if (s.size() > z.size())return INF;
	if (s == z)return 0;
	int ret = INF;
	REP(i, n) {
		string tmp = s;
		REP(j, tmp.size() ) {
			if (j+a[i].size()<=tmp.size()&&tmp.substr(j, a[i].size()) == a[i]) {
				REP(k, a[i].size())tmp.erase(tmp.begin() + j);
				REP(k, b[i].size())tmp.insert(tmp.begin() + j+k,b[i][k]);
				j += b[i].size()-1;
			}
		}
		if (tmp != s) {
			ret = min(ret, dfs(tmp, a, b) + 1);
		}
	}
	return ret;

}
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	while (cin >> n, n) {
		vector<string> a(n), b(n);
		REP(i, n) cin >> a[i] >> b[i];

		cin >> y >> z;
		int c = dfs(y, a, b);
		if (c == INF)cout << -1 << endl;
		else cout << c << endl;
	}
}