#include <stdio.h>

void chmax(int* a, int b)
{
	if (*a < b) *a = b;
}

int main()
{
	int N;
	char S[200001];
	scanf("%d", &N);
	scanf("%s", S);
	
	int i, k, ans[2][200003], anss[2][200003], flag;
	for (i = 0, k = 0, flag = 0, ans[0][0] = 0, anss[0][0] = 0; i < N; i++) {
		ans[0][i+1] = ans[0][i];
		anss[0][i+1] = ans[0][i+1];
		if (k == 0) {
			if (S[i] == '(') k = 2;
			else if (S[i] == '?') {
				if (S[i+1] == '?' || S[i+1] == ')') k = 2;
			}
		} else {
			if (S[i] == '(') k++;
			else {
				k--;
				flag = 1;
				anss[0][i+1] = ans[0][i+1] + 1;
				if (k == 0) {
					ans[0][i+1]++;
					flag = 0;
				}
			}
		}
	}
	ans[0][N+1] = ans[0][N];
	if (flag == 1) ans[0][N+1]++;
	
	for (i = N - 1, k = 0, flag = 0, ans[1][N+1] = 0, anss[1][N+1] = 0; i >= 0; i--) {
		ans[1][i+1] = ans[1][i+2];
		anss[1][i+1] = ans[1][i+1];
		if (k == 0) {
			if (S[i] == ')') k = 2;
			else if (S[i] == '?') {
				if (i > 0 && (S[i-1] == '?' || S[i-1] == '(')) k = 2;
			}
		} else {
			if (S[i] == ')') k++;
			else {
				k--;
				flag = 1;
				anss[1][i+1] = ans[1][i+1] + 1;
				if (k == 0) {
					ans[1][i+1]++;
					flag = 0;
				}
			}
		}
	}
	ans[1][0] = ans[1][1];
	if (flag == 1) ans[1][0]++;
	
	int max = 0;
	for (i = 0; i <= N; i++) {
		chmax(&max, ans[0][i] + anss[1][i+1]);
		chmax(&max, anss[0][i] + ans[1][i+1]);
	}
	printf("%d\n", max);
	fflush(stdout);
	return 0;
}