#include <iostream>
#include <vector>
#include <algorithm>
#include <stack>
#include <cstring>
#include <queue>

#define ll long long
#define MAX(a,b) (a)>(b)?(a):(b)
#define MIN(a,b) (a)>(b)?(b):(a)
#define pll pair<ll, ll>

using namespace std;

typedef struct route {
	int u, v;
	ll cost;

	route(int a, int b, ll c): u(a), v(b), cost(c){}

	bool operator < (const route& a) const {
		return this->cost > a.cost;
	}

};

int N, M;
char univ[1234];
priority_queue<route, vector<route>, less<route>> G;
int parent[1234], _rank[1234];
bool vi[1234];

void init() {
	for (int i = 0; i <= N; i++) {
		parent[i] = i;
		_rank[i] = 0;
	}
}

int find(int x) {
	if (parent[x] == x)
		return x;
	else {
		return parent[x] = find(parent[x]);
	}
}

void unite(int a, int b) {
	a = find(a);
	b = find(b);

	if (a == b) return;

	if (_rank[a] < _rank[b]) {
		parent[b] = a;
	}
	else {
		parent[a] = b;

		if (_rank[a] == _rank[b]) {
			_rank[a]++;
		}
	}
}

int main(void)
{
	cin >> N >> M;

	ll ans = 0;
	init();

	for (int i = 1; i <= N; i++)
		scanf(" %c ", &univ[i]);

	for (int i = 0; i < M; i++) {
		int u, v, c;
		cin >> u >> v >> c;
		if (univ[u] != univ[v]) {
			G.push(route(u, v, c));
		}
	}

	while (!G.empty()) {
		int u = G.top().u, v = G.top().v, c = G.top().cost;
		G.pop();

		if (find(u) != find(v)) {
			unite(u, v);
			vi[u] = true;
			vi[v] = true;
			ans += c;
		}
	}

	for (int i = 1; i <= N; i++) {
		if (vi[i] == false) {
			printf("-1\n");
			return 0;
		}
	}

	printf("%lld\n", ans);


	return 0;
}