package contest161028; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.InputMismatchException; public class D { InputStream is; PrintWriter out; String INPUT = ""; void solve() { int n = ni(); char[] s = ns().toCharArray(); int[] from = new int[n - 1]; int[] to = new int[n - 1]; for (int i = 0; i < n - 1; i++) { from[i] = ni() - 1; to[i] = ni() - 1; } int[][] g = packU(n, from, to); int[][] pars = parents3(g, 0); int[] par = pars[0], ord = pars[1], dep = pars[2]; int[] des = new int[n]; for(int i = n-1;i >= 0;i--){ int cur = ord[i]; des[cur]++; if(i > 0)des[par[cur]] += des[cur]; } int[] dpw = new int[n]; for(int i = n-1;i >= 0;i--){ int cur = ord[i]; if(s[cur] == 'w'){ dpw[cur]++; } if(i > 0)dpw[par[cur]] += dpw[cur]; } int allw = dpw[0]; int allc = n - allw; long ret = 0; for(int i = 0;i < n;i++){ if(s[i] == 'w'){ ret += (long)(allw-1)*allc; int wsum = 0; int csum = 0; for(int e : g[i]){ if(par[i] == e)continue; ret -= (long)dpw[e] * (des[e]-dpw[e]); wsum += dpw[e]; csum += des[e]-dpw[e]; } ret -= (long)(allw-1-wsum)*(allc-csum); } } out.println(ret); } public static int[][] parents3(int[][] g, int root) { int n = g.length; int[] par = new int[n]; Arrays.fill(par, -1); int[] depth = new int[n]; depth[0] = 0; int[] q = new int[n]; q[0] = root; for (int p = 0, r = 1; p < r; p++) { int cur = q[p]; for (int nex : g[cur]) { if (par[cur] != nex) { q[r++] = nex; par[nex] = cur; depth[nex] = depth[cur] + 1; } } } return new int[][] { par, q, depth }; } static int[][] packU(int n, int[] from, int[] to) { int[][] g = new int[n][]; int[] p = new int[n]; for (int f : from) p[f]++; for (int t : to) p[t]++; for (int i = 0; i < n; i++) g[i] = new int[p[i]]; for (int i = 0; i < from.length; i++) { g[from[i]][--p[from[i]]] = to[i]; g[to[i]][--p[to[i]]] = from[i]; } return g; } void run() throws Exception { is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); long s = System.currentTimeMillis(); solve(); out.flush(); if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){ // @Override // public void run() { // long s = System.currentTimeMillis(); // solve(); // out.flush(); // if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // } // }; // t.start(); // t.join(); } public static void main(String[] args) throws Exception { new D().run(); } private byte[] inbuf = new byte[1024]; public int lenbuf = 0, ptrbuf = 0; private int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private double nd() { return Double.parseDouble(ns()); } private char nc() { return (char)skip(); } private String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private long[] nal(int n) { long[] a = new long[n]; for(int i = 0;i < n;i++)a[i] = nl(); return a; } private char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private int[][] nmi(int n, int m) { int[][] map = new int[n][]; for(int i = 0;i < n;i++)map[i] = na(m); return map; } private int ni() { return (int)nl(); } private long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); } }