class in{struct myIterator{int it;const bool rev;explicit constexpr myIterator(int it_, bool rev=false):it(it_),rev(rev){}int operator*(){return it;}bool operator!=(myIterator& r){return it!=r.it;}void operator++(){rev?--it:++it;}};const myIterator i,n;public:explicit constexpr in(int n):i(0),n(n){}explicit constexpr in(int i,int n):i(i,n<i),n(n){}const myIterator& begin(){return i;}const myIterator& end(){return n;}};

#include <bits/stdc++.h>
using namespace std;
// input
int n;
string s;
vector<vector<int>> adj;
// end input
using i64 = long long;
i64 cSum, wSum, ans;
pair<i64/*c*/, i64/*w*/> dfs(int cur, int par) {
    i64 partC = 0LL, partW = 0LL;
    bool is_w = s[cur] == 'w';
    for(int nv : adj[cur]) {
        if(nv == par) continue;
        i64 c, w;
        tie(c, w) = dfs(nv, cur);
        if(is_w)
          ans += c * (wSum - w - 1LL);
        partC += c;
        partW += w;
    }
    if(is_w)
      ans += partW * (cSum - partC);
    if(is_w) partW++; else partC++;
    return make_pair(partC, partW);
}
int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin >> n;
    cin >> s;
    adj.resize(n);
    for(int _ : in(n - 1)) {
        int a, b;
        cin >> a >> b;
        --a; --b;
        adj[a].emplace_back(b);
        adj[b].emplace_back(a);
    }
    ans = cSum = wSum = 0LL;
    for(char c : s) {
        if(c == 'c') ++cSum;
        else ++wSum;
    }
    dfs(0, -1);
    cout << ans << endl;
}