import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		long curtime=System.currentTimeMillis();
		new Main().run();
		System.err.println(System.currentTimeMillis()-curtime);
	}
	
	long ans=0;
	int totW=0,totC=0;
	
	void dfs(int cur,int par,ArrayList<Integer>[] g,int[] c,int[] w,char[] cs) {
		if(cs[cur]=='c')++c[cur];
		else ++w[cur];
		for(int dst:g[cur]) {
			if(dst==par)continue;
			dfs(dst,cur,g,c,w,cs);
			c[cur]+=c[dst];
			w[cur]+=w[dst];
		}
		if(cs[cur]=='w') {
			for(int dst:g[cur]) {
				if(dst==par)continue;
				ans+=(long)c[dst]*(totW-w[dst]-1);
			}
		}
		if(cs[cur]=='w')ans+=(long)(totC-c[cur])*(w[cur]-1);
	}
	
	void run() {
		Scanner sc=new Scanner(System.in);
		int N=sc.nextInt();//3<=N<=1e5
		char[] cs=sc.next().toCharArray();
		ArrayList<Integer>[] g=new ArrayList[N];
		for(int i=0;i<g.length;++i)g[i]=new ArrayList<>();
		for(int i=0;i<N-1;++i) {
			int a=sc.nextInt();
			int b=sc.nextInt();
			--a;--b;
			g[a].add(b);
			g[b].add(a);
		} 
		int[] c=new int[N];
		int[] w=new int[N];
		for(char ch:cs)if(ch=='c')++totC; else ++totW;;
		dfs(0,-1,g,c,w,cs);
		System.out.println(ans);
	}
	
	void tr(Object...objects) {System.out.println(Arrays.deepToString(objects));}
}