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#include <bits/stdc++.h>
using namespace std;
typedef int64_t ll;
const int MX=2e5+6;
int dp[55][55];
string h;
bool balanced(int x,int y)
{
    if(h[x]=='('&&h[y]==')')return 1;
    if(h[x]=='['&&h[y]==']')return 1;
    if(x==y)return 1;
    return 0;
}
int correct(int x,int y)
{
    if(h[x]=='('||h[x]=='[')return 1;
    if(h[y]==']'||h[y]==')')return 1;
    return 2;
}
int solve(int l=0,int r=(int)h.size()-1)
{
    if(r-l==-1)return 0;
    if(r<l)return 1e5;
    if(l==r)return 1e5;
    if(dp[l][r]!=-1)return dp[l][r];
    int ans=1e5;
    if(balanced(l,r))ans=min(ans,solve(l+1,r-1));
    if(!balanced(l,r))ans=min(ans,correct(l,r)+solve(l+1,r-1));
    for(int i=l+1;i<r;i++)
    {
        if(balanced(l,i)&&balanced(i+1,r))
        {
            ans=min(ans,solve(l,i)+solve(i+1,r));
        }
        if(balanced(l,i)&&!balanced(i+1,r))
        {
            ans=min(ans,solve(l,i)+solve(i+1,r)+correct(i+1,r));
        }
        if(!balanced(l,i)&&balanced(i+1,r))
        {
            ans=min(ans,solve(l,i)+solve(i+1,r)+correct(l,i));
        }
        if(!balanced(l,i)&&!balanced(i+1,r))
        {
            ans=min(ans,solve(l,i)+solve(i+1,r)+correct(l,i)+correct(i+1,r));
        }
    }
    return dp[l][r]=ans;
}
 int main()
{
    memset(dp,-1,sizeof dp);
    cin>>h;
    cout<<solve();
   return 0;
}