// 2009アジア地区予選 B : Repeated Substitution with Sed
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <set>
#include <queue>

using namespace std;

string replaceAll(string s, string a, string b){
	for(int p=s.find(a);p!=-1;p=s.find(a,p+b.size()))
		s.replace(p, a.size(), b);
	return s;
}

int search(vector<string> a, vector<string> b, string c, string d){
	queue< pair<string, int> > qu; qu.push(make_pair(c,0));
	set<string> S; S.insert(c);
	while(!qu.empty()){
		pair<string, int> p = qu.front(); qu.pop();
		for(int i=0;i<a.size();i++){
			string t = replaceAll(p.first, a[i], b[i]);
			if(t == d) return p.second + 1;
			if(t.size()<d.size()&&S.find(t)==S.end()){
				S.insert(t);
				qu.push(make_pair(t,p.second+1));
			}
		}
	}
	return -1;
}

int main(){
	ifstream fin("B.in");
	int n;
	while(fin >> n, n){
		vector<string> a(n), b(n);
		for(int i=0;i<n;i++) fin >> a[i] >> b[i];
		string c, d;
		fin >> c >> d;
		cout << search(a, b, c, d) << endl;
	}
}