from sys import stdin
input = stdin.readline
from random import randrange
from heapq import heappush, heappop

base1, base2 = 10**5*5, 5
def encode(d, n, c):
    return d*base1+n*base2+c

base3 = 10**5
def decode(n):
    return n//base1, n//base2%base3, n%base2

N, M = map(int, input().split())
G = [[] for _ in range(N)]
for _ in range(M):
    u, v, c = map(int, input().split())
    u, v = u-1, v-1
    G[u].append((v, c))
S = input().rstrip("\n")

KCPC = "KCPC"

INF = 1<<60

def func(color):
    c = 0 if KCPC[0] != "K" else 1
    dist = [[INF]*5 for _ in range(N)]
    dist[0][0] = 0
    visited = [[False]*5 for _ in range(N)]
    que = [encode(0, 0, 0)]
    while que:
        d, n, c = decode(heappop(que))
        if visited[n][c]:
            continue
        visited[n][c] = True
        for next, weight in G[n]:
            nc = c+1 if c < 4 and KCPC[c] == S[next] and (S[next] != "C" or c//2 == color[next]) else c
            if dist[n][c]+weight < dist[next][nc]:
                dist[next][nc] = dist[n][c]+weight
                heappush(que, encode(dist[next][nc], next, nc))
    return dist

ans = INF
for _ in range(20):
    dist = func([randrange(2) for _ in range(N)])
    MIN = min(dist[i][-1] for i in range(N))
    ans = min(ans, MIN)

print(ans if ans != INF else -1)