//#pragma GCC target("avx2")
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using pli = pair<ll,int>;
#define AMARI 998244353
//#define AMARI 1000000007
#define el '\n'
#define El '\n'
#define YESNO(x) ((x) ? "Yes" : "No")
#define YES YESNO(true)
#define NO YESNO(false)
#define REV_PRIORITY_QUEUE(tp) priority_queue<tp,vector<tp>,greater<tp>>
#define EXIT_ANS(x) {cout << (x) << '\n'; return;}
template <typename T> void inline SORT(vector<T> &v){sort(v.begin(),v.end()); return;}
template <typename T> void inline VEC_UNIQ(vector<T> &v){sort(v.begin(),v.end()); v.erase(unique(v.begin(),v.end()),v.end()); return;}
template <typename T> T inline MAX(vector<T> &v){return *max_element(v.begin(),v.end());}
template <typename T> T inline MIN(vector<T> &v){return *min_element(v.begin(),v.end());}
template <typename T> T inline SUM(vector<T> &v){T ans = 0; for(int i = 0; i < (int)v.size(); i++)ans += v[i]; return ans;}
void inline TEST(void){cerr << "TEST" << endl; return;}
template <typename T> bool inline chmin(T &x,T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}
template <typename T> bool inline chmax(T &x,T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template <typename T = long long> vector<T> inline get_vec(int n){
    vector<T> ans(n);
    for(int i = 0; i < n; i++)cin >> ans[i];
    return ans;
}
template <typename T> void inline print_vec(vector<T> &vec,bool kaigyou = false){
    int n = (int)vec.size();
    for(int i = 0; i < n; i++){
        cout << vec[i];
        if(kaigyou || i == n - 1)cout << '\n';
        else cout << ' ';
    }
    if(!n)cout << '\n';
    return;
}
template <typename T> void inline debug_vec(vector<T> &vec,bool kaigyou = false){
    int n = (int)vec.size();
    for(int i = 0; i < n; i++){
        cerr << vec[i];
        if(kaigyou || i == n - 1)cerr << '\n';
        else cerr << ' ';
    }
    if(!n)cerr << '\n';
    return;
}
vector<vector<int>> inline get_graph(int n,int m = -1,bool direct = false){
    if(m == -1)m = n - 1;
    vector<vector<int>> g(n);
    while(m--){
        int u,v;
        cin >> u >> v;
        u--; v--;
        g[u].push_back(v);
        if(!direct)g[v].push_back(u);
    }
    return g;
}

#define MULTI_TEST_CASE false
void solve(void){
    //問題を見たらまず「この問題設定から言えること」をいっぱい言う
    //よりシンプルな問題に言い換えられたら、言い換えた先の問題を自然言語ではっきりと書く
    //複数の解法のアイデアを思いついた時は全部メモしておく
    //g++ -D_GLIBCXX_DEBUG -Wall -O2 e.cpp -o o
    int n;
    cin >> n;
    string s;
    cin >> s;
    int r,m;
    cin >> r >> m;
    int cnt = 0;
    for(int i = 0; i < n; i++){
        if(s[i] == '(')cnt++;
    }
    int cc = n - cnt;
    if(n % 2){
        EXIT_ANS(-1);
        return;
    }
    int dif = abs(cnt - cc);
    cout << dif / 2 << el;
    return;
}

void calc(void){
    return;
}

signed main(void){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    calc();
    int t = 1;
    if(MULTI_TEST_CASE)cin >> t;
    while(t--){
        solve();
    }
    return 0;
}