import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.complex, std.container, std.math, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


int N;
string S;
int[] A, B;

int[][] G;
int[] par;
long[][] dp, DP;

void dfs0(int u, int p) {
  par[u] = p;
  foreach (v; G[u]) {
    if (v != p) {
      dfs0(v, u);
    }
  }
  dp[u] = [0, 0];
  ++dp[u]["cw".indexOf(S[u])];
  foreach (v; G[u]) {
    if (v != p) {
      dp[u][] += dp[v][];
    }
  }
}

void dfs1(int u, int p) {
  long[] sum = [0, 0];
  ++sum["cw".indexOf(S[u])];
  if (p != -1) {
    sum[] += DP[u][];
  }
  foreach (v; G[u]) {
    if (v != p) {
      sum[] += dp[v][];
    }
  }
  foreach (v; G[u]) {
    if (v != p) {
      DP[v][] = sum[] - dp[v][];
    }
  }
  foreach (v; G[u]) {
    if (v != p) {
      dfs1(v, u);
    }
  }
}

void main() {
  try {
    for (; ; ) {
      N = readInt();
      S = readToken();
      A = new int[N - 1];
      B = new int[N - 1];
      foreach (i; 0 .. N - 1) {
        A[i] = readInt() - 1;
        B[i] = readInt() - 1;
      }
      
      G = new int[][N];
      foreach (i; 0 .. N - 1) {
        G[A[i]] ~= B[i];
        G[B[i]] ~= A[i];
      }
      par = new int[N];
      dp = new long[][](N, 2);
      DP = new long[][](N, 2);
      const rt = 0;
      dfs0(rt, -1);
      dfs1(rt, -1);
      debug {
        writeln("rt = ", rt);
        writeln("dp = ", dp);
        writeln("DP = ", DP);
      }
      long ans;
      foreach (u; 0 .. N) {
        if (S[u] == 'w') {
          long[] sum = [0, 0];
          if (par[u] != -1) {
            sum[] += DP[u][];
          }
          foreach (v; G[u]) {
            if (v != par[u]) {
              sum[] += dp[v][];
            }
          }
          if (par[u] != -1) {
            ans += DP[u][0] * (sum[1] - DP[u][1]);
          }
          foreach (v; G[u]) {
            if (v != par[u]) {
              ans += dp[v][0] * (sum[1] - dp[v][1]);
            }
          }
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}