#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
#define rep(i, l, r) for ((i) = (l); (i) <=(r); (i)++)
#define rep1(i, r, l) for ((i) = (r); (i) >=(l); (i)--)
int main()
{
	ios_base::sync_with_stdio(false) ; 
	cin.tie(NULL);
    cout.tie(NULL);
    ll t ; 
    cin>>t;
    while(t--)
    {
        string s ; 
        cin>>s;
        ll n = s.length() ; 
    
        if(n%2!=0)
        {
            cout<<"-1";
        }
        else
        {
          ll i ; ll a1=0;
          ll a0=0;
          rep(i,0,n-1)
          {
              if(s[i]=='1')
              {
                  a1++;
              }
              else
              {
                  a0++;
              }
          }
            if(a1==n || a0==n)
            {
                cout<<"-1";
            }
            else
            {
            ll g = n/2 ; 
            ll y1 = abs(g-a1);
            ll y2 = abs(g-a0);
            ll yep = min(y1,y2);
            cout<<yep ; 
            }
        }
        cout<<"\n";
    }
     
     
      							
	return 0;
}