import sys
sys.setrecursionlimit(1000000)

n = int(input())
s = input()
G = [[] for _ in range(n)]
for m in range(n-1):
    x, y = [int(i) for i in input().split()]
    x -= 1
    y -= 1
    G[x].append(y)
    G[y].append(x)

nc = s.count('c')
nw = s.count('w')

dp1 = [[0,0] for _ in range(n)]
def dfs1(u, p):
    dp1[u][0] = 1 if s[u] == 'c' else 0
    dp1[u][1] = 1 if s[u] == 'w' else 0

    res = 0
    for to in G[u]:
        if to == p: continue
        res += dfs1(to, u)
        dp1[u][0] += dp1[to][0]
        dp1[u][1] += dp1[to][1]
        if s[u] == 'w':
            res += dp1[to][0] * (nw - dp1[to][1] - 1)
    if s[u] == 'w':
        res += (nc - dp1[u][0]) * (dp1[u][1] - 1)
    return res

print(dfs1(0,-1))