bool M1;
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdlib>
#include<climits>
#include<iomanip>
#include<cassert>
#include<random>
#include<cstdio>
#include<vector>
#include<bitset>
#include<stack>
#include<queue>
#include<deque>
#include<cmath>
#include<ctime>
#include<map>
#include<set>
//#include<ext/pb_ds/assoc_container.hpp>
//#include<ext/pb_ds/hash_policy.hpp>
//#include<ext/pb_ds/priority_queue.hpp>
#define fi first
#define se second
#define LD double
#define name(x) #x
#define ll long long
#define Vector Point
#define I128 __int128
#define ull unsigned ll
#define pii pair<int,int>
#define pb(x) push_back(x)
#define dek(x) debug(x)<<" "
#define deh(x) debug(x)<<endl
#define syt cerr<<"sytakioi\n"
#define debug(x) cout<<name(x)<<":"<<x
#define F(i,a,b) for(int i=a,i##end=b;i<=i##end;++i)
#define UF(i,a,b) for(int i=a,i##end=b;i>=i##end;--i)
#define look_memory cerr<<abs(&M2-&M1)/1024.0/1024<<'\n'
#define rd_i(l,r) uniform_int_distribution<int>(l,r)(rd)
#define rd_r(l,r) uniform_real_distribution<double>(l,r)(rd)
#define look_time cerr<<(clock()-Time)*1.0/CLOCKS_PER_SEC<<'\n'
using namespace std;
//using namespace __gnu_cxx;
mt19937 rd(time(0));
int num0,num1;
string s,t;
namespace sub1{
inline void mian(){
	F(i,0,s.size()-1) if(s[i]==t[0]) return void(cout<<"-1\n");
	cout<<"0\n";
}
}
namespace sub2{
inline void solve1(){
	int num=0;
	F(i,1,s.size()-1) if(s[i]=='1'&&s[i-1]=='0') ++num;
	cout<<num<<'\n';
}
inline void solve2(){
	int num=0,ans=0;
	F(i,0,s.size()-1) num+=s[i]-'0';
	if(num<s.size()/2) return void(cout<<"-1\n");
	F(i,1,s.size()-1) if(s[i]=='0'&&s[i-1]=='0') ++ans;
	cout<<ans<<'\n';
}
inline void mian(){
	if(t[0]=='1'){
		t[0]^=1;t[1]^=1;
		F(i,0,s.size()-1) s[i]^=1;
	}
	if(t[0]!=t[1]) solve1();
	else solve2();
}
}
namespace sub3{
inline void solve1(){
	int ans=0;
	F(i,2,s.size()-1) if(s[i-2]=='1'&&s[i-1]=='0'&&s[i]=='0') ++ans;
	cout<<ans<<'\n';
}
inline void solve2(){
	int ans=0;
	F(i,2,s.size()-1) if(s[i-2]=='0'&&s[i-1]=='1'&&s[i]=='0') ++ans;
	cout<<(ans+1)/2<<'\n';
}
inline void solve3(){
	int num=0,ans=0;
	F(i,0,s.size()-1) num+=s[i]-'0';
	if(1) return void(cout<<"-1\n");
	num=0;
	F(i,0,s.size()-1){
		if(s[i]=='0') ++num;
		else{
			if(num>=3) ans+=(num-2)/3+1;
			num=0;
		}
	}
	cout<<ans<<'\n';
}
inline void mian(){
	if(t=="100") solve1();
	else if(t=="001"){
		reverse(s.begin(),s.end());
		reverse(t.begin(),t.end());
		solve1();
	}else if(t=="010") solve2();
	else solve3();
}
}
bool M2;
int main(){
	int Time=clock();
	look_memory;
	cin.tie(nullptr)->sync_with_stdio(false);
	cin>>s>>t;
	if(s.size()<t.size()) return cout<<"0\n",0;
	F(i,0,t.size()-1)
		if(t[i]=='0') ++num0;
		else ++num1;
	if(num1>num0){
		F(i,0,t.size()-1) t[i]^=1;
		F(i,0,s.size()-1) s[i]^=1;
	}
	if(t.size()==1) sub1::mian();
	else if(t.size()==2) sub2::mian();
	else sub3::mian();
	look_time;
	return 0;
}