#include <iostream>
#include <string>
#include <vector>
using namespace std;
const int INF = 1e9;
bool match(char a, char b){
	return (a == '(' && b == ')') || (a == '[' && b == ']');
}
int main(){
    string s;
    cin >> s;
    int n = s.size();
    vector<vector<int>> dp(s.size() + 2, vector<int>(s.size() + 2, 1));
    for(int l = 2; l <= n; l++){
    	for(int i = 0; i < n - l + 1; i++){
    		int j = i + l - 1;
    		dp[i][j] = INF; 
    		for(int k = i; k < j; k++){
    			dp[i][j] = min(dp[i][j], dp[i][k] + dp[k + 1][j]);
			}
			if(match(s[i], s[j])) {
				if (i + 1 <= j - 1)
                    dp[i][j] = min(dp[i][j], dp[i+1][j-1]);
                else
                    dp[i][j] = 0; // 两个相邻的括号直接匹配
            }
		}
	}
	cout << dp[0][n - 1] << endl;
    return 0;
}