#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

int main()
{
    int n;
    string s;
    cin >> n >> s;
    vector<vector<int> > edges(n);
    for(int i=0; i<n-1; ++i){
        int a, b;
        cin >> a >> b;
        -- a;
        -- b;
        edges[a].push_back(b);
        edges[b].push_back(a);
    }

    queue<pair<int, int> > q;
    stack<pair<int, int> > stk;
    q.push(make_pair(0, -1));
    while(!q.empty()){
        pair<int, int> p = q.front();
        q.pop();
        stk.push(p);

        int curr = p.first;
        int prev = p.second;
        for(int next : edges[curr]){
            if(next != prev)
                q.push(make_pair(next, curr));
        }
    }

    int cSum = count(s.begin(), s.end(), 'c');
    int wSum = n - cSum;
    vector<int> cCnt(n, 0), wCnt(n, 0);
    long long ans = 0;
    while(!stk.empty()){
        pair<int, int> p = stk.top();
        stk.pop();

        int curr = p.first;
        int parent = p.second;
        for(int child : edges[curr]){
            if(child != parent){
                cCnt[curr] += cCnt[child];
                wCnt[curr] += wCnt[child];
            }
        }
        if(s[curr] == 'c'){
            ++ cCnt[curr];
            continue;
        }
        
        ++ wCnt[curr];
        ans += (wCnt[curr] - 1LL) * (cSum - cCnt[curr]);
        for(int child : edges[curr]){
            if(child != parent){
                ans += cCnt[child] * (wSum - wCnt[child] - 1LL);
            }
        }
    }
    cout << ans << endl;

    return 0;
}