## https://yukicoder.me/problems/no/3561

import heapq

MAX_INT = 10 ** 18

def main():
    N, M = map(int, input().split())
    next_nodes = [[] for _ in range(N)]
    for _ in range(M):
        u, v, c = map(int, input().split())
        next_nodes[u - 1].append((v - 1, c))
    S = input()

    fix = [[MAX_INT for _ in range(N)] for _ in range(4)]
    seen = [[MAX_INT for _ in range(N)] for _ in range(4)]
    queue = []

    answer = MAX_INT
    seen[0][0] = 0
    heapq.heappush(queue, (0, 0, 0))
    while len(queue) > 0:
        cost, state, v = heapq.heappop(queue)
        if fix[state][v] < MAX_INT:
            continue

        fix[state][v] = cost
        if state == 0 and S[v] == "K":
            new_state = 1
            if seen[new_state][v] > cost:
                seen[new_state][v] = cost
                heapq.heappush(queue, (cost, new_state, v))
        elif state == 1 and S[v] == "C":
            new_state = 2
            if seen[new_state][v] > cost:
                seen[new_state][v] = cost
                heapq.heappush(queue, (cost, new_state, v))
        elif state == 2 and S[v] == "P":
            new_state = 3
            if seen[new_state][v] > cost:
                seen[new_state][v] = cost
                heapq.heappush(queue, (cost, new_state, v))
        elif state == 3 and S[v] == "C":
            answer = min(answer, cost)
        
        for w, c in next_nodes[v]:
            if fix[state][w] < MAX_INT:
                continue

            new_cost = c + cost
            if seen[state][w] > new_cost:
                seen[state][w] = new_cost
                heapq.heappush(queue, (new_cost, state, w))
    
    if answer == MAX_INT:
        print(-1)
    else:
        print(answer)










if __name__ == "__main__":
    main()