import java.io.*; import java.util.*; public class Main_yukicoder439_1 { private static Scanner sc; private static Printer pr; private static void solve() { int n = sc.nextInt(); char[] s = sc.next().toCharArray(); List> edges = new ArrayList<>(n); for (int i = 0; i < n; i++) { edges.add(new ArrayList<>()); } for (int i = 0; i < n - 1; i++) { int a = sc.nextInt() - 1; int b = sc.nextInt() - 1; edges.get(a).add(b); edges.get(b).add(a); } boolean[] used = new boolean[n]; int[] p = new int[n]; long[] cw = new long[n]; long[] cww = new long[n]; Arrays.fill(p, -1); int root = 0; p[root] = root; Deque st = new ArrayDeque<>(); st.push(root); while (!st.isEmpty()) { int e = st.peek(); if (used[e]) { st.pop(); if (s[e] == 'w') { cw[e]++; } if (e != p[e]) { cw[p[e]] += cw[e]; cww[p[e]] += cww[e]; if (s[p[e]] == 'w') { cww[p[e]] += cw[e]; } } } else { used[e] = true; for (int next : edges.get(e)) { if (p[next] != -1) { continue; } st.push(next); p[next] = e; } } } Arrays.fill(p, -1); p[root] = root; // long[] pw = new long[n]; long[] pww = new long[n]; long tw = cw[root]; // long tww = cww[root]; st = new ArrayDeque<>(); st.push(root); long ans = 0; while (!st.isEmpty()) { int e = st.pop(); for (int next : edges.get(e)) { if (p[next] != -1) { continue; } st.push(next); p[next] = e; } if (e != root) { long tmp = cww[p[e]] - cww[e]; if (s[p[e]] == 'w') { tmp -= cw[e]; } if (s[e] == 'c') { pww[e] += pww[p[e]]; pww[e] += tmp; } else { pww[e] += pww[p[e]]; pww[e] += tw - cw[e]; pww[e] += tmp; } } if (s[e] == 'c') { ans += pww[e]; ans += cww[e]; } } pr.println(ans); } // --------------------------------------------------- public static void main(String[] args) { sc = new Scanner(System.in); pr = new Printer(System.out); solve(); pr.close(); sc.close(); } @SuppressWarnings("unused") private static class Scanner { BufferedReader br; Scanner (InputStream in) { br = new BufferedReader(new InputStreamReader(in)); } private boolean isPrintable(int ch) { return ch >= '!' && ch <= '~'; } private boolean isCRLF(int ch) { return ch == '\n' || ch == '\r' || ch == -1; } private int nextPrintable() { try { int ch; while (!isPrintable(ch = br.read())) { if (ch == -1) { throw new NoSuchElementException(); } } return ch; } catch (IOException e) { throw new NoSuchElementException(); } } String next() { try { int ch = nextPrintable(); StringBuilder sb = new StringBuilder(); do { sb.appendCodePoint(ch); } while (isPrintable(ch = br.read())); return sb.toString(); } catch (IOException e) { throw new NoSuchElementException(); } } int nextInt() { try { // parseInt from Integer.parseInt() boolean negative = false; int res = 0; int limit = -Integer.MAX_VALUE; int radix = 10; int fc = nextPrintable(); if (fc < '0') { if (fc == '-') { negative = true; limit = Integer.MIN_VALUE; } else if (fc != '+') { throw new NumberFormatException(); } fc = br.read(); } int multmin = limit / radix; int ch = fc; do { int digit = ch - '0'; if (digit < 0 || digit >= radix) { throw new NumberFormatException(); } if (res < multmin) { throw new NumberFormatException(); } res *= radix; if (res < limit + digit) { throw new NumberFormatException(); } res -= digit; } while (isPrintable(ch = br.read())); return negative ? res : -res; } catch (IOException e) { throw new NoSuchElementException(); } } long nextLong() { try { // parseLong from Long.parseLong() boolean negative = false; long res = 0; long limit = -Long.MAX_VALUE; int radix = 10; int fc = nextPrintable(); if (fc < '0') { if (fc == '-') { negative = true; limit = Long.MIN_VALUE; } else if (fc != '+') { throw new NumberFormatException(); } fc = br.read(); } long multmin = limit / radix; int ch = fc; do { int digit = ch - '0'; if (digit < 0 || digit >= radix) { throw new NumberFormatException(); } if (res < multmin) { throw new NumberFormatException(); } res *= radix; if (res < limit + digit) { throw new NumberFormatException(); } res -= digit; } while (isPrintable(ch = br.read())); return negative ? res : -res; } catch (IOException e) { throw new NoSuchElementException(); } } float nextFloat() { return Float.parseFloat(next()); } double nextDouble() { return Double.parseDouble(next()); } String nextLine() { try { int ch; while (isCRLF(ch = br.read())) { if (ch == -1) { throw new NoSuchElementException(); } } StringBuilder sb = new StringBuilder(); do { sb.appendCodePoint(ch); } while (!isCRLF(ch = br.read())); return sb.toString(); } catch (IOException e) { throw new NoSuchElementException(); } } void close() { try { br.close(); } catch (IOException e) { // throw new NoSuchElementException(); } } } private static class Printer extends PrintWriter { Printer(PrintStream out) { super(out); } } }