#include <bits/stdc++.h>
using namespace std;

#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
#define x first
#define y second
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)

typedef long long ll;
typedef double db;
typedef long double LD;
typedef pair<int, int> pii;
typedef pair<db, db> pdd;
typedef pair<ll, ll> pll;

const int N = 5e3 + 47;
vector<int> g[N];
bool vis[N];

int solve()
{
	int n;
	string s;
	if (!(cin >> n >> s))
		return 1;
	
	map<char, char> op;
	op[')'] = '(';
	op[']'] = '[';
	op['}'] = '{';
	fill(g, g + n, vector<int>());
	FOR (i, 0, n - 1)
	{
		int a, b;
		cin >> a >> b;
		--a;--b;
		g[a].pb(b);
		g[b].pb(a);
	}
	
	int ans = 0;
	auto bfs = [&](int v) -> void
	{
		queue<pair<int, string>> q;
		q.push({v, string(1, s[v])});
		fill(vis, vis + n, false);
		while (!q.empty())
		{
			auto top = q.front();
			q.pop();
			int u = top.x;
			if (vis[u])
				continue;
			string str = top.y;
			if (str.empty())
				ans++;
			vis[u] = 1;
			for (int to: g[u])
			{
				if (!vis[to])
				{
					char c = s[to];
					if (!op.count(c))
					{
						q.push({to, str + s[to]});
					}
					else
					{
						if (str.empty() || str.back() != op[c])
						{
							vis[to] = 1;
						}
						else
						{
							string nx = str;
							nx.pop_back();
							q.push({to, nx});
						}
					}
					
				}
			}
		}
	};
	
	FOR (i, 0, n)
	{
		bfs(i);
	}
	cout << ans << '\n';
	
	return 0;
}

int32_t main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int TET = 1e9;
	//cin >> TET;
	for (int i = 1; i <= TET; i++)
	{
		if (solve())
		{
			break;
		}
		#ifdef ONPC
			cerr << "_____________________________\n";
		#endif
	}
	#ifdef ONPC
		cerr << "\nfinished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec\n";
	#endif
	return 0;
}