import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)

def dfs(cur, prev=-1):
    global res
    
    cs = []
    ws = []
    
    for nn in adj_list[cur]:
        if nn != prev:
            c, w = dfs(nn, cur)
            cs.append(c)
            ws.append(w)
    
    if S[cur] == 'c':
        return sum(cs)+1, sum(ws)
    elif S[cur] == 'w':
        cs.append(total_c-sum(cs))
        ws.append(total_w-sum(ws)-1)
        sum_w = sum(ws)
        
        for c, w in zip(cs, ws):
            res += c*(sum_w-w)
        
        return sum(cs[:-1]), sum_w-ws[-1]+1

N = int(input())
S = input()
total_c = S.count('c')
total_w = S.count('w')
adj_list = [[] for _ in range(N)]

for _ in range(N-1):
    a, b = map(int, input().split())
    adj_list[a-1].append(b-1)
    adj_list[b-1].append(a-1)

res = 0
dfs(0)

print(res)