from heapq import *
def main():
    n, m = list(map(int, input().split()))
    node = [[] for _ in range(n)]
    for _ in range(m):
        u, v, w = list(map(int, input().split()))
        node[u-1].append((v-1, w))
    S = input()
    inf = 1 << 60
    dp = [[inf for _ in range(6)] for _ in range(n)]
    ep = [[-1 for _ in range(6)] for _ in range(n)]
    dp[0][0] = 0
    hq = []
    heappush(hq, (0, 0, 0))
    while hq:
        c, now, f = heappop(hq)
        if dp[now][f] < c: continue
        if f == 0:
            if S[now] == "K" and dp[now][1] > c:
                heappush(hq, (c, now, 1))
        elif f == 1:
            if S[now] == "C":
                if dp[now][2] > c:
                    if ep[now][2] != -1 and ep[now][2] != now:
                        ep[now][3] = ep[now][2]
                        dp[now][3] = dp[now][2]
                        heappush(hq, (dp[now][3], now, 3))
                    ep[now][2] = now
                    dp[now][2] = c
                    heappush(hq, (dp[now][2], now, 2))
                elif dp[now][3] > c and ep[now][2] != c:
                    ep[now][3] = now
                    dp[now][3] = c
                    heappush(hq, (dp[now][3], now, 3))
        elif f == 2 or f == 3:
            if S[now] == "P":
                if dp[now][4] > c:
                    if ep[now][4] != -1 and ep[now][4] != now:
                        ep[now][5] = ep[now][4]
                        dp[now][5] = dp[now][4]
                        heappush(hq, (dp[now][5], now, 5))
                    ep[now][4] = now
                    dp[now][4] = c
                    heappush(hq, (dp[now][4], now, 4))
                elif dp[now][5] > c and ep[now][4] != c:
                    ep[now][5] = now
                    dp[now][5] = c
                    heappush(hq, (dp[now][5], now, 5))
        else:
            if S[now] == "C" and ep[now][f] != now:
                return c
        for nxt, w in node[now]:
            if dp[nxt][f] > c+w:
                dp[nxt][f] = c+w
                heappush(hq, (c+w, nxt, f))
    return -1

print(main())