#include <iostream>
using namespace std;
const int N=1e2+10;
string s;
int dp[N][N];
int main(){
	cin>>s;
	int n=s.length();
	for(int i=n-2;i>=0;i--){
		for(int j=0;j<n;j++){
			if((s[i]=='('&&s[j]==')')||(s[i]=='['&&s[j]==']'))
				dp[i][j]=dp[i+1][j-1]+2;
			for(int k=i;k<j;k++){
				dp[i][j]=max(dp[i][j],dp[i][k]+dp[k+1][j]);
			} 
		}
	}
	cout<<n-dp[0][n-1]<<endl;
}