#include <bits/stdc++.h>
using namespace std;
#define M 300005
int n,m,ty;
char S[5];
vector<int>edge[M];
using ll = long long;
ll f[M][3][3];
using pll = pair<ll,ll>;
vector<pll>A;
ll solve1(){//C(#a,2) + sum
    vector<ll>p;
    ll ret = 0, s = 0;
    for(auto [x,y]: A) 
        s += y, p.push_back(x-y);
    sort(p.begin(),p.end());
    reverse(p.begin(),p.end());
    ret = s;
    for(int i=0;i<p.size();i++){
        s += p[i];
        ret = max(ret,(1ll*i*(i+1)>>1)+s);
    }
    return ret;
}
using tll = tuple<ll,ll,ll>;
vector<tll>B;
vector<tll>add[M];
ll solve2(){
    int cnt = 0,sz = B.size();
    for(int i=0;i<=sz;i++)add[i].clear();
    ll ret = 0,s = 0,s_set = 0;
    multiset<ll>S1,S2,D;
    for(auto [x,y,z]:B){
        s += x;
        ret += max(y,z);
        s_set += max(y,z) - x;
        if(y > z && y - z < sz) add[y-z].push_back(tll(x,y,z));
        if(z >= y) S2.insert(z-x);
        else S1.insert(y-x);
    }
    for(int i=1;i<=sz;i++){
        s_set += S2.size();
        while(!D.empty() && !S1.empty() && *D.rbegin()+i == *S1.begin()){
            S1.erase(S1.begin());
            auto it = D.end();--it;
            D.erase(it);
        }
        if(S1.empty()){
            s_set -= (*S2.begin())+i;
            S2.erase(S2.begin());
        }else if(S2.empty()){
            s_set -= (*S1.begin());
            S1.erase(S1.begin());
        }else if((*S1.begin()) <= (*S2.begin()) + i){
            s_set -= (*S1.begin());
            S1.erase(S1.begin());
        }else{
            s_set -= (*S2.begin())+i;
            S2.erase(S2.begin());
        }
        for(auto [x,y,z]: add[i]){
            if(S1.count(y-x))S1.erase(S1.lower_bound(y-x)),S2.insert(z-x);
            else D.insert(z-x);
        }
        ret = max(ret, s + s_set);
    }
    return ret;
}
void dfs(int F,int now){
    for(int &to:edge[now])if(to!=F){
        dfs(now,to);
    }
    if(ty == 1){
        for(int a=0;a<2;a++)
            for(int b=0;b<2;b++){
                if(a == 0){
                    A.clear();
                    for(int &to:edge[now])if(to!=F)
                        A.push_back(pll(f[to][0][a]+(a==0&&b==1),f[to][1][a]+(a==0&&b==0)));
                    f[now][a][b] = solve1();
                }else {
                    for(int &to:edge[now])if(to!=F)
                        f[now][a][b] += max(f[to][0][a],f[to][1][a]);
                }
            }
    }else{
        for(int a=0;a<3;a++)
            for(int b=0;b<3;b++){
                if(a == 1){
                    B.clear();
                    for(int &to:edge[now])if(to!=F)
                        B.push_back(tll(f[to][0][a]+(b==2),f[to][1][a],f[to][2][a]+(b==0)));
                    f[now][a][b] = solve2();
                }else {
                    for(int &to:edge[now])if(to!=F)
                        f[now][a][b] += max(f[to][0][a],f[to][1][a]);
                }
            }
    }
}
ll redfs(int F,int now,int flg){
    ll ret = 0,sz=edge[now].size();
    // if(flg)cout<<now<<' '<<sz<<endl;
    if(flg) ret += sz*(sz-1);
    for(int &to:edge[now])if(to!=F)
        ret += redfs(now,to,!flg);
    return ret;
}
int main(){
    cin>>n;
    scanf("%s",S+1);
    m=strlen(S+1);
    if(m==1)cout<<n<<endl;
    else if(m==2)cout<<n-1<<endl;
    if(m<=2)return 0;
    for(int a,b,i=1;i<n;i++){
        scanf("%d%d",&a,&b);
        edge[a].push_back(b);
        edge[b].push_back(a);
    }
    if(S[1] == S[3]){
        cout<<max(redfs(0,1,0),redfs(0,1,1))<<endl;
        return 0;
    }
    if(S[1]!=S[2] && S[2]!=S[3] && S[1]!=S[3])S[1]='a',S[2]='b',S[3]='c',ty=1;
    else S[1]='a',S[2]='a',S[3]='b',ty=2;
    dfs(0,1);
    if(ty == 1){
        cout<<max(f[1][0][1],max(f[1][1][1],f[1][2][1]))<<endl;
    }else{
        ll ans = 0;
        int a = 0;
        {
            A.clear();
            for(int &to:edge[1])
                A.push_back(pll(f[to][0][a],f[to][1][a]));
            ans = solve1();
        }
        a = 1;
        {
            ll s = 0;
            for(int &to:edge[1])
                s += max(f[to][0][a],f[to][1][a]);
            ans = max(ans,s);
        }
        cout<<ans<<endl;
    }
    return 0;
}