#include <stdio.h>

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