import java.util.Scanner;
class Trie{
    int k =1;
    private Node root;
    public Trie() {
        root = new Node();
    }
    int insert(String str){
        Node t = root;
        int idx;
        for(int i=0;i<str.length();i++){
            if(str.charAt(i)>=‘a‘&&str.charAt(i)<=‘z‘){
                idx = str.charAt(i)-‘a‘;
            }else{
                idx = str.charAt(i)-‘A‘+26;
            }
            if(t.nodes[idx]==null){
                Node node = new Node();
                t.nodes[idx] = node;
            }
            t = t.nodes[idx];
        }
        if(t.id==0) t.id = k++;
        return t.id;
    }
    class Node{
         Node [] nodes;
         int id;
         public Node() {
             nodes = new Node[52];
             id = 0;
         }
    }
}

public class Main {
    static int [][] map;
    static boolean [] vis;
    static int [] low;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int n = sc.nextInt();
            if(n==-1) break;
            map = new int[155][155];
            low = new int[155];
            vis = new boolean[155];
            for(int i=0;i<155;i++){
                for(int j=0;j<155;j++){
                    map[i][j] = 999999999;
                }
            }
            Trie tree = new Trie();
            String str1,str2;
            str1 = sc.next();str2 = sc.next();
            int start = tree.insert(str1);
            int end = tree.insert(str2);
            for(int i=0;i<n;i++){
                str1 = sc.next();
                str2 = sc.next();
                int a = tree.insert(str1);
                int b = tree.insert(str2);
                int c = sc.nextInt();
                map[a][b] = map[b][a] = c;  
            }
            int k = tree.k;
            int cost = dij(start, end, k);
            if(cost>=999999999) System.out.println(-1);
            else System.out.println(cost);
        }
    }
    static int dij(int pos,int end,int n){
        for(int i=0;i<n;i++){
            low[i] = map[pos][i];
            vis[i] = false;
        }
        vis[pos] = true;
        low[pos] = 0;
        for(int i=1;i<n;i++){
            int Min = 999999999;
            for(int j=0;j<n;j++){
                if(Min>low[j]&&!vis[j]){
                    pos = j;
                    Min = low[j];
                }
            }
            vis[pos] = true;
            for(int j=0;j<n;j++){
                if(low[j]>low[pos]+map[pos][j]&&!vis[j]){
                    low[j]=low[pos]+map[pos][j];
                }
            }
        }
        return low[end];
    }
}