#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a, b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define pb push_back
#define show(x) cout <<#x<<" = "<<(x)<<endl
#define spair(p) cout <<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout <<" "<<kbrni;cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 100005;

string s;
int alc,alw;
vector<int> G[MAX_N];
int memc[MAX_N],memw[MAX_N];
ll ans;

void dfs(int u,int p)
{
    if(G[u].size() == 1 && G[u][0] == p){
        if(s[u] == 'c'){
            memc[u] = 1;
            memw[u] = 0;
        }else{
            memc[u] = 0;
            memw[u] = 1;
        }
        return;
    }
    if(memc[u] >= 0 && memw[u] >= 0){
        return;
    }
    int smc = 0,smw = 0;
    rep(i,G[u].size()){
        if(G[u][i] != p){
            dfs(G[u][i],u);
            smc += memc[G[u][i]];
            smw += memw[G[u][i]];
        }
    }
    if(s[u] == 'c'){
        memc[u] = smc+1;
        memw[u] = smw;
    }else{
        memc[u] = smc;
        memw[u] = smw+1;
        int remc = alc - memc[u];
        int remw = alw - memw[u];
        rep(i,G[u].size()){
            if(G[u][i] != p){
                ans += (ll)memc[G[u][i]] * (alw-memw[G[u][i]]-1);
            }else{
                ans += (ll)remc*(alw-remw-1);
            }
        }
    }
}

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    cin >> s;
    rep(i,n){
        if(s[i] == 'c'){
            alc++;
        }else{
            alw++;
        }
    }
    rep(i,n-1){
        int a,b;
        cin >> a >> b;
        G[a-1].pb(b-1);
        G[b-1].pb(a-1);
    }
    rep(i,n){
        memc[i] = memw[i] = -1;
    }
    dfs(0,-1);
    cout << ans << endl;
    return 0;
}