#include<bits/stdc++.h>
#define ll long long
#define db double
#define ull unsigned long long
#define pb push_back
#define pii pair<int, int>
#define FR first
#define SE second
#define int long long
using namespace std;
inline int read() {
  int x = 0; bool op = false;
  char c = getchar();
  while(!isdigit(c))op |= (c == '-'), c = getchar();
  while(isdigit(c))x = (x << 1) + (x << 3) + (c ^ 48), c = getchar();
  return op ? -x : x;
}
const int N = 3e5 + 10;
int n;
vector<int> G[N];
char s[5];
namespace A {
  void MAIN() {
    printf("%lld\n", n);
    return ;
  }
};
namespace AA {
  void MAIN() {
    printf("%lld\n", 2 * (n - 1));
    return ;
  }
};
namespace AB {
  void MAIN() {
    printf("%lld\n", n - 1);
    return ;
  }
};
namespace AAA {
  void MAIN() {
    int ans = 0;
    for(int i = 1; i <= n; i++)ans += G[i].size() * (G[i].size() - 1);
    printf("%lld\n", ans);
  }
};
namespace AAB {
  int ans = 0;
  int f[N][2], g[N];
  void dfs(int u, int fa) {
    int sum0 = 0;
    vector<int> A;
    for(int v : G[u]) {
      if(v == fa)continue;
      dfs(v, u);
      g[u] += max(g[v], f[v][1]);
      sum0 += g[v]; A.pb(f[v][0] - g[v]);
    }
    if(u == 1)ans = max(ans, g[u]);
    sort(A.begin(), A.end(), greater<int>());
    for(int j = 1; j < A.size(); j++)A[j] += A[j - 1];
    for(int o = 0; o < 2; o++)
      for(int j = 0; j <= A.size(); j++) {
        f[u][o] = max(f[u][o], sum0 + (j ? A[j - 1] : 0) + (j + !o) * ((int)A.size() - j + o));
        if(u == 1)ans = max(ans, sum0 + (j ? A[j - 1] : 0) + j * ((int)A.size() - j));
      }
    return ;
  }
  void MAIN() {
    dfs(1, 0);
    printf("%lld\n", ans);
    return ;
  }
};
namespace ABA {
  int ans = 0;
  int f[N][2], g[N];
  void dfs(int u, int fa) {
    int sum0 = 0;
    vector<int> A;
    for(int v : G[u]) {
      if(v == fa)continue;
      dfs(v, u);
      g[u] += max(g[v], f[v][0]);
      sum0 += f[v][1]; A.pb(g[v] - f[v][1]);
    }
    if(u == 1)ans = max(ans, g[u]);
    sort(A.begin(), A.end(), greater<int>());
    for(int j = 1; j < A.size(); j++)A[j] += A[j - 1];
    for(int o = 0; o < 2; o++)
      for(int j = 0; j <= A.size(); j++) {
        f[u][o] = max(f[u][o], sum0 + (j ? A[j - 1] : 0) + (j + !o) * (j + !o - 1));
        if(u == 1)ans = max(ans, sum0 + (j ? A[j - 1] : 0) + j * (j - 1));
      }
    return ;
  }
  void MAIN() {
    dfs(1, 0);
    printf("%lld\n", ans);
    return ;
  }
};
namespace ABC {
  int ans = 0;
  int f[N][2], g[N];
  void dfs(int u, int fa) {
    int sum0 = 0;
    vector<int> A;
    for(int v : G[u]) {
      if(v == fa)continue;
      dfs(v, u);
      g[u] += max(g[v], f[v][0]);
      sum0 += f[u][1]; A.pb(g[v] - f[u][1]);
    }
    if(u == 1)ans = max(ans, g[u]);
    sort(A.begin(), A.end(), greater<int>());
    for(int j = 1; j < A.size(); j++)A[j] += A[j - 1];
    for(int o = 0; o < 2; o++)
      for(int j = 0; j <= A.size(); j++) {
        f[u][o] = max(f[u][o], sum0 + (j ? A[j - 1] : 0) + ((j + !o) / 2) * (j + !o - (j + !o) / 2));
        if(u == 1)ans = max(ans, sum0 + (j ? A[j - 1] : 0) + (j / 2) * (j - (j / 2)));
      }
    return ;
  }
  void MAIN() {
    dfs(1, 0);
    printf("%lld\n", ans);
    return ;
  }
};
signed main() {
  n = read();
  scanf("%s", s);
  for(int i = 1; i < n; i++) {
    int u = read(), v = read();
    G[u].pb(v); G[v].pb(u);
  }
  if(strlen(s) == 1)return A::MAIN(), 0;
  if(strlen(s) == 2) {
    if(s[0] == s[1])return AA::MAIN(), 0;
    else return AB::MAIN(), 0;
  }
  if(strlen(s) == 3) {
    if(s[0] == s[1] && s[1] == s[2])return AAA::MAIN(), 0;
    if(s[0] == s[1] || s[1] == s[2])return AAB::MAIN(), 0;
    if(s[0] == s[2])return ABA::MAIN(), 0;
    return ABC::MAIN(), 0;
  }
  return 0;
}