#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int N;
string S;
int dp[202020];
vector<int> A;
void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>S;
	int cur=0;
	string T=S;
	A={0};
	FOR(i,N) {
		if(S[i]=='?') {
			if(cur||i!=A.back()) {
				T[i]=')';
			}
			else {
				if(i==N-1||S[i+1]!='(') {
					T[i]='(';
				}
				else {
					T[i]=')';
				}
			}
		}
		if(T[i]=='(') {
			cur++;
		}
		else if(T[i]==')') {
			cur--;
			if(cur<0) {
				cur=0;
				if(i!=A.back()) A.push_back(i+1);
			}
		}
	}
	T=S;
	int ret=A.size()-1+(A.back()!=N);
	int num=0,prev=N;
	cur=0;
	T=S;
	for(i=N-1;i>=0;i--) {
		if(S[i]=='?') {
			if(cur||prev!=i+1) {
				T[i]='(';
			}
			else {
				if(i==0||S[i-1]!=')') {
					T[i]=')';
				}
				else {
					T[i]='(';
				}
			}
		}
		if(T[i]==')') {
			cur++;
		}
		else if(T[i]=='(') {
			cur--;
			if(cur<0) {
				cur=0;
				if(i+1!=prev) num++;
				prev=i;
				
				x=lower_bound(ALL(A),i)-A.begin()-1;
				ret=max(ret,num+x+(A[x]-1!=i));
			}
		}
	}
	cout<<ret<<endl;
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}