#include <bits/stdc++.h>
	#define pb push_back
	using namespace std;
 
	int main(){
	    int t = 1;
	    //cin >> t;

	    while(t--){
	    	int n, m;
	    	cin >> n >> m;

	    	map<int,vector<pair<int,int>>>mp;

	    	for(int i = 0 ; i < m ; i++){
	    		int u, vv, w;
	    		scanf("%d%d%d",&u, &vv, &w);

	    		mp[u].pb(make_pair(vv,w));
	    		mp[vv].pb(make_pair(u, w));
	    	}

	    	string s;
	    	cin >> s;

	    	bool f = 0;
	    	long long ans = INT_MAX;

	    	for(int i = 1 ; i <= n ; i++){
	    		for(int j = 0 ; j < mp[i].size() ; j++){
	    			if(s[mp[i][j].first - 1] == s[i - 1]){
	    				ans = min((int)ans, mp[i][j].second);
	    				f = 1;
	    			}
	    			int num = mp[i][j].first;
	    			vector<int>temp;

	    			for(int k = 0 ; k < mp[num].size() ; k++){
	    				
	    				if(s[mp[num][k].first - 1] == s[i - 1] && mp[num][k].first != i){
	    					temp.pb(mp[num][k].second);
	    				}
	    			}
	    			if(temp.size() > 0){
	    				f = 1;
	    				for(int l = 0 ; l < temp.size() ; l++){
	    					//cout<<temp[l]<<" "<<mp[i][j].second<<endl;
	    					ans = min(ans, (long long)temp[l] + mp[i][j].second);
	    				}
	    			}
	    			temp.clear();
	    		}

	    	}

	    	if(f)
	    	cout<<ans<<endl;
	    	else puts("-1");
	    }
	}