import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.*;



public class Main {
	static final int INF = 2 << 28;
	static final long INF_L = 2L << 60;
	static final int  MOD = 1000000007;
	static final long MOD_L = 1000000007L;
	static final int[] vx_4 = {1,0,-1,0};
	static final int[] vy_4 = {0,-1,0,1};
	static final int[] vx_5 = {1,0,-1,0,0};
	static final int[] vy_5 = {0,1,0,-1,0};
	static final int[] vx_8 = {1,1,1,0,0,-1,-1,-1};
	static final int[] vy_8 = {1,0,-1,1,-1,1,0,-1};
	static final int[] vx_9 = {1,1,1,0,0,0,-1,-1,-1};
	static final int[] vy_9 = {1,0,-1,1,0,-1,1,0,-1};

	public static void main(String[] args) {	
		//FastScanner sc = new FastScanner();
		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		while(true) {
			int n = sc.nextInt();
			if(n == 0) break;
			String[] a = new String[n];
			String[] b = new String[n];
			for(int i = 0; i < n; i++) {
				a[i] = sc.next();
				b[i] = sc.next();
			}
			String g = sc.next();
			String d = sc.next();
			
			int min = dfs(a,b,g,d,0);
			if(min == INF) min = -1;
			System.out.println(min);
		}
	}
	static int dfs(String[] a, String[] b, String g, String d, int cost) {
		if(g.length() > d.length()) return INF;
		if(g.length() == d.length() && g.equals(d)) return cost;
		int ret = INF;
		for(int i = 0; i < a.length; i++) {
			StringBuffer next = new StringBuffer();
			StringBuffer tmp  = new StringBuffer(g);
			boolean ok = false;
			while(tmp.length() != 0) {
				if(tmp.length() >= a[i].length() && tmp.substring(0, a[i].length()).equals(a[i])) {
					next.append(b[i]);
					tmp.delete(0, a[i].length());
					ok = true;
				}
				else {
					next.append(tmp.substring(0, 1));
					tmp.delete(0, 1);
				}
			}
			if(ok) ret = Math.min(dfs(a,b,next.toString(),d,cost+1),ret);
		}
		return ret;
		
	}

}





class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
    public boolean hasNext() { skipUnprintable(); return hasNextByte();}
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    public int nextInt() {
    	if (!hasNext()) throw new NoSuchElementException();
        int n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
}

Measured memory_bytes: 118876