#include <bits/stdc++.h>
using namespace std;
const int N = 1e3 + 5;
int n;
int dp[N][N], root[N][N];
int a[N];
string s;

bool check(int l, int r)
{
	return ((s[l] == '(' && s[r] == ')') || (s[l] == '[' && s[r] == ']')); 
}

int main()
{
	memset(dp, 0x3f, sizeof(dp));
	cin >> s;
	int len = s.size();
	s = " " + s;
	for(int i = 1; i <= len; i++)
		dp[i][i] = 1;
	for(int i = 2; i <= len; i++)
	{
		for(int l = 1; l + i - 1 <= len; l++)
		{
			int r = i + l - 1;
			if(l + 1 == r && check(l, r))
				dp[l][r] = 0; 
			if(l + 1 < r && check(l, r)) 
				dp[l][r] = dp[l + 1][r - 1];
			for(int k = l; k < r; k++)
			{
				dp[l][r] = min(dp[l][r], dp[l][k] + dp[k + 1][r]);	
			}
		}
	}
	cout << dp[1][len] << endl;
	return 0; 
}