// what is matter? never mind. 
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,sse4,popcnt,abm,mmx,avx,avx2") 
#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(int i=(a);i>=(b);--i)
#define ll long long
#define int long long
#define ull unsigned long long
#define SZ(x) ((int)((x).size()))
#define ALL(x) (x).begin(),(x).end()
using namespace std;
inline int read()
{
    char c=getchar();int x=0;bool f=0;
    for(;!isdigit(c);c=getchar())f^=!(c^45);
    for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
    if(f)x=-x;return x;
}

#define mod 1000000007
struct modint{
	int x;
	modint(int o=0){x=o;}
	modint &operator = (int o){return x=o,*this;}
	modint &operator +=(modint o){return x=x+o.x>=mod?x+o.x-mod:x+o.x,*this;}
	modint &operator -=(modint o){return x=x-o.x<0?x-o.x+mod:x-o.x,*this;}
	modint &operator *=(modint o){return x=1ll*x*o.x%mod,*this;}
	modint &operator ^=(int b){
		modint a=*this,c=1;
		for(;b;b>>=1,a*=a)if(b&1)c*=a;
		return x=c.x,*this;
	}
	modint &operator /=(modint o){return *this *=o^=mod-2;}
	friend modint operator +(modint a,modint b){return a+=b;}
	friend modint operator -(modint a,modint b){return a-=b;}
	friend modint operator *(modint a,modint b){return a*=b;}
	friend modint operator /(modint a,modint b){return a/=b;}
	friend modint operator ^(modint a,int b){return a^=b;}
	friend bool operator ==(modint a,modint b){return a.x==b.x;}
	friend bool operator !=(modint a,modint b){return a.x!=b.x;}
	bool operator ! () {return !x;}
	modint operator - () {return x?mod-x:0;}
	bool operator <(const modint&b)const{return x<b.x;}
};
inline modint qpow(modint x,int y){return x^y;}

vector<modint> fac,ifac,iv;
inline void initC(int n)
{
	if(iv.empty())fac=ifac=iv=vector<modint>(2,1);
	int m=iv.size(); ++n;
	if(m>=n)return;
	iv.resize(n),fac.resize(n),ifac.resize(n);
	For(i,m,n-1){
		iv[i]=iv[mod%i]*(mod-mod/i);
		fac[i]=fac[i-1]*i,ifac[i]=ifac[i-1]*iv[i];
	}
}
inline modint C(int n,int m){
	if(m<0||n<m)return 0;
	return initC(n),fac[n]*ifac[m]*ifac[n-m];
}
inline modint sign(int n){return (n&1)?(mod-1):(1);}

#define fi first
#define se second
#define pb push_back
#define mkp make_pair
typedef pair<int,int>pii;
typedef vector<int>vi;

#define maxn 300005
#define inf 0x3f3f3f3f

int n,res;
string s;
vi e[maxn];

string op;
int F(int x){
	if(op=="ABA") return x*(x-1);
	if(op=="ABC") return (x/2)*(x-x/2);
	exit(233);
}
int F2(int x,int y){
	return x*y;
}

// self , fa
int f[maxn][2][2];
void dfs(int u,int pa){
	int s[2]={0,0};
	vi p[2];
	for(int v:e[u]){
		if(v==pa)continue;
		dfs(v,u);
		For(j,0,1) {
			s[j]+=f[v][0][j];
			p[j].pb(f[v][1][j]-f[v][0][j]);
		}
	}
	For(j,0,1) sort(ALL(p[j]),greater<int>());
//	cout<<"u: "<<u<<"\n";
	For(i,0,1) For(j,0,1) {
		int now=p[i].size(),sum=s[i];
		f[u][i][j]=sum+(i?F((!j)+now):0ll);
		for(int k:p[i]){
			--now;
			sum+=k;
			f[u][i][j]=max(f[u][i][j],sum+(i?F((!j)+now):0ll));
		}
	}
	if(u==1) res=max(f[u][0][1],f[u][1][1]);
}

void dfs2(int u,int pa){
	int s[2]={0,0};
	vi p[2];
	for(int v:e[u]){
		if(v==pa)continue;
		dfs2(v,u);
		For(j,0,1) {
			s[j]+=f[v][0][j];
			p[j].pb(f[v][1][j]-f[v][0][j]);
		}
	}
	For(j,0,1) sort(ALL(p[j]),greater<int>());
	For(i,0,1) For(j,0,1) {
		int now=p[i].size(),sum=s[i],sz=p[i].size();
		f[u][i][j]=sum+(i?F2((!j)+now,j+sz-now):0ll);
		if(u==1) res=max(res,sum+(i?F2(now,sz-now):0ll));
		for(int k:p[i]){
			--now;
			sum+=k;
			f[u][i][j]=max(f[u][i][j],sum+(i?F2((!j)+now,j+sz-now):0ll));
			if(u==1) res=max(res,sum+(i?F2(now,sz-now):0ll));
		}
	}
}

void work()
{
	n=read();
	cin>>s;
	For(i,2,n){
		int u=read(),v=read();
		e[u].pb(v),e[v].pb(u);
	}
	if(s.size()==1){
		cout<<n<<"\n";
	}
	else if(s.size()==2){
		if(s[0]==s[1]) cout<<2*(n-1)<<"\n";
		else cout<<(n-1)<<"\n";
	}
	else{
		if(s[0]==s[1] && s[1]==s[2]){
			int res=0;
			For(i,1,n) res+=e[i].size()*(e[i].size()-1);
			cout<<res<<"\n";
			return;
		}
		else if((s[0]==s[1] && s[1]!=s[2]) || (s[1]==s[2] && s[0]!=s[1])){
			op="AAB";
		}
		else if(s[0]==s[2] && s[0]!=s[1]){
			op="ABA";
		}
		else {
			For(i,0,2)For(j,i+1,2)assert(s[i]!=s[j]);
			op="ABC";
		}
		if(op=="AAB")dfs2(1,0);
		else dfs(1,0);
		cout<<res<<"\n";
	}
}

signed main()
{
	int T=1;
	while(T--)work();
	return 0;
}
/*

*/