/** gnu specific **/
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
/** contains everything I need in std **/
#include <bits/stdc++.h>

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(S) ((int)S.size())
#define FOR(i, st_, n) for(int i = st_; i < n; ++i)
#define RFOR(i, n, end_) for(int i = (n)-1; i >= end_; --i)
#define x first
#define y second
#define pb push_back
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef unsigned long long ull;
typedef long double LD;
typedef pair<ull, ull> pull;
using namespace __gnu_pbds;
typedef tree<ll, null_type, less<>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
using namespace std;
#ifdef ONPC
mt19937 rnd(228);
#else
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
#endif

vector<vector<int>> adj;
string s;

bool is_open(char ch)
{
	return ch=='{'||ch=='('||ch=='[';
}

bool match(char op, char cl)
{
	return (op=='{'&&cl=='}') || (op=='('&&cl==')') || (op=='['&&cl==']');
}


vector<pair<int, char>> st;
int p=-1;
int f(int v, int pr)
{
	int res=0;
	int pr_p=p;

	if(is_open(s[v]))
	{
		st.pb({p, s[v]});
		p = sz(st)-1;
	}
	else
	{
		if(st.empty() || !match(st[p].y, s[v]))
			return 0;
		else
		{
			st.pb({p,s[v]});
			p = st[p].x;
		}
		if(p==-1)++res;
	}
	for(auto to: adj[v])
	{
		if(to!=pr)
		{
			res += f(to, v);
		}
	}
	st.pop_back();
	p=pr_p;
	return res;
}

int solve()
{
	int n;
	if(!(cin>>n))return 1;
	cin>>s;
	adj=vector<vector<int>>(n);
	FOR(_,0,n-1)
	{
		int a, b;
		cin>>a>>b;
		--a,--b;
		adj[a].pb(b);
		adj[b].pb(a);
	}
	ll res=0;
	FOR(root,0,n)
	{
		p=-1;
		res += f(root,-1);
	}
	cout<<res<<'\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
        cout << "__________________________" << endl;
#endif
    }
#ifdef ONPC
    cerr << endl << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl;
#endif
}