#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
int op(int a, int b) { return min(a, b); }
int e() { return INF; }
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	string s, t; cin >> s;
	int r, m; cin >> r >> m;
	if (n % 2 != 0) {
		cout << -1 << endl;
		return 0;
	}
	int d = 0;
	rep(i, n) {
		if (s[i] == '(')d++;
		else d--;
	}
	int ans = abs(d/2) * m;
	cout << ans << endl;
	/*t = s + s;
	if (n % 2 != 0) {
		cout << -1 << endl;
		return 0;
	}
	vector<int>v(2 * n + 1);
	rep(i, 2 * n) {
		v[i + 1] = v[i];
		if (s[i] == '(')v[i + 1]++;
		else v[i + 1]--;
	}
	segtree<int, op, e>seg(v);
	int ans = INF;
	rep(i, n) {
		int l = i + 1;
		int r = l + n;
		auto get = seg.prod(l, r);
		cout << v[i] << " " << get << endl;
		auto tmp = max(0, v[i] - get);
		chmin(ans, tmp*m);
	}
	cout << ans << endl;*/
	return 0;
}