{.optimization: speed.} import strutils, sequtils var n = stdin.readline.parseint s = stdin.readline g = newSeqWith(n, newSeq[int]()) for i in 0..n-2: var tmp = stdin.readline.split.map(parseint) (a, b) = (tmp[0]-1, tmp[1]-1) g[a].add(b) g[b].add(a) var c = newSeq[int64](n) w = newSeq[int64](n) cAll = s.count('c') wAll = s.count('w') proc dfs(cur, prev: int): int64 = if s[cur] == 'c': c[cur] = 1 else: w[cur] = 1 for i in g[cur]: if i == prev: continue result += dfs(i, cur) c[cur] += c[i] w[cur] += w[i] if s[cur] == 'w': result += c[i]*(wAll-1-w[i]) if prev != -1 and s[cur] == 'w': result += (cAll-c[cur])*(w[cur]-1) dfs(0, -1).echo