import std.algorithm, std.conv, std.range, std.stdio, std.string;
import std.container; // SList, DList, BinaryHeap

void main()
{
  auto n = readln.chomp.to!int;
  auto s = readln.chomp;

  auto children = new int[][](n);
  foreach (_; 0..n-1) {
    auto rd = readln.splitter;
    auto a = rd.front.to!int-1; rd.popFront();
    auto b = rd.front.to!int-1;
    children[a] ~= b;
    children[b] ~= a;
  }

  auto parent = new int[](n);
  parent[0] = -1;

  auto ac = new int[](n), aw = new int[](n);

  auto q = DList!int(0), st = SList!int();
  while (!q.empty) {
    auto u = q.front; q.removeFront();
    st.insertFront(u);
    foreach (v; children[u])
      if (v != parent[u]) {
        parent[v] = u;
        ac[v] = ac[u] + (s[u] == 'c');
        aw[v] = aw[u] + (s[u] == 'w');
        q.insertBack(v);
      }
  }

  auto dc = new int[](n), dw = new int[](n);

  while (!st.empty) {
    auto u = st.front; st.removeFront();
    foreach (v; children[u])
      if (v != parent[u]) {
        dc[u] += dc[v] + (s[v] == 'c');
        dw[u] += dw[v] + (s[v] == 'w');
      }
  }

  auto ans = 0L;
  foreach (u; 0..n)
    if (s[u] == 'w') {
      ans += long(ac[u]) * dw[u];
      ans += long(aw[u]) * dc[u];
      ans += long(dc[u]) * dw[u];
      foreach (v; children[u])
        if (v != parent[u])
          ans -= long(dc[v] + (s[v] == 'c')) * (dw[v] + (s[v] == 'w'));
    }

  writeln(ans);
}