#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+1)*((int)p.size()-i-1))+s);
    }
    return ret;
}
using tll = tuple<ll,ll,ll>;
vector<tll>B;
const ll inf = 1e16;
ll solve2(){
    if(B.empty()) return 0ll;
    vector<ll>p;
    ll ret = 0, sumz = 0,v = -inf;
    for(auto [x,y,z]: B){
        sumz += y;
        if(v == -inf) v = x - z;
        else assert(v == x-z);
        p.push_back(z - y);
    }
    sort(p.begin(),p.end());
    reverse(p.begin(),p.end());
    static ll pre[M];
    pre[0]=0;
    for(int i=0;i<p.size();i++)pre[i+1] = pre[i] + p[i];
    ret = sumz;
    // cout<<pre[n]<<' '<<v<<endl;
    for(int i=0;i<p.size();i++){
        int n = (int)p.size() - i; 
        int p = max(0,(n-1)>>1);
        ret = max(ret,1ll*p*(n-p) + sumz + max(pre[n] + v*(n-p),pre[n] + v*p));
        // cout<<p<<endl;
        p++;
        if(p<=n)ret = max(ret,1ll*p*(n-p) + sumz + max(pre[n] + v*(n-p),pre[n] + v*p));
    }
    // for(auto [x,y,z]: B)cout<<x<<','<<y<<','<<z<<endl;
    // cout<<ret<<endl;
    return ret;
}
void dfs(int F,int now){
    for(int &to:edge[now])if(to!=F){
        dfs(now,to);
    }
    if(ty == 2){
        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]+(b==1),f[to][1][a]+(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][2][a],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;
        A.clear();
        for(int &to:edge[1])
            A.push_back(pll(f[to][0][0],f[to][1][0]));
        ans = solve1();
        
        ll s = 0;
        for(int &to:edge[1])
            s += max(f[to][0][1],f[to][1][1]);
        ans = max(ans,s);
        cout<<ans<<endl;
    }
    return 0;
}