#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
#include <functional>
using namespace std;

#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair((a),(b))
#define pb(a) push_back(a)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<(x)<<endl
#define fi first
#define se second

#define INF 2147483600

vector<vector<int> > vec;
vector<char> label;
vector<long> memoc, memow;
int sumc, sumw;

long dfs(int from, int d){
  long tmpc=0, tmpw=0, ret=0;
  for(auto i : vec[d]) if(i != from){
    ret += dfs(d, i);
    tmpc += memoc[i];
    tmpw += memow[i];
  }
  memoc[d] = tmpc + (label[d]=='c');
  memow[d] = tmpw + (label[d]=='w');

  if(label[d]=='w'){
    for(auto i : vec[d]) if(i != from){
      ret += memoc[i] * (sumw-memow[i]-1);
      ret += memow[i] * (sumc-memoc[i]);
    }
    ret += tmpc * (sumw-tmpw-1);
    ret += tmpw * (sumc-tmpc);
  }

  return ret;
}

int main(){
  int n;
  scanf("%d\n", &n);
  vec = vector<vector<int> >(n,vector<int>());
  label = vector<char>(n);
  rep(i,n) scanf("%c", &label[i]);
  rep(i,n-1){
    int a,b;
    scanf("%d %d", &a, &b);
    a--; b--;
    vec[a].pb(b);
    vec[b].pb(a);
  }
  sumc=0; sumw=0;
  rep(i,n){
    if(label[i]=='c') sumc++;
    else sumw++;
  }

  memoc = vector<long>(n, 0);
  memow = vector<long>(n, 0);

  cout<<dfs(-1, 0)/2<<endl;

  return 0;
}