//HEZ NOIP模拟 8.16 T2
#include <bits/stdc++.h>
using namespace std;
const int N=2e5+5;
int a[N],b[N],n,m;
string s,t;
int sub1()
{
	for(int i=0;i<n;i++)if(s[i]==t[0])return -1;
	return 0;
}
int sub2()
{
	int res=0;
	while(n&&s[n-1]==t[0])n--;
	for(int i=0;i<n;i++)res+=(s[i]==t[0]&&s[i+1]!=t[0]);
	return res;
}
int sub3()
{
	int cnt=0,res=0;
	for(int i=0;i<n;i++)cnt+=(s[i]==t[0]);
	if(cnt>(n+1)/2)return -1;
	for(int i=1;i<n;i++)res+=(s[i]==t[0]&&s[i]==s[i-1]);
	return res;
}
int sub4()
{
	if(t[0]!=t[1])
	{
		reverse(s.begin(),s.end());
		reverse(t.begin(),t.end());
	}
	int res=0;
	while(n&&s[n-1]==t[0])n--;
	for(int i=1;i<n-1;i++)res+=(s[i]==t[0]&&s[i-1]==s[i]&&s[i+1]!=t[0]);
	return res;
}
int sub5()
{
	int ans=0;
	for(int i=1;i<n-1;i++)ans+=(s[i]==t[1]&&s[i-1]!=s[i]&&s[i+1]!=s[i]);
	return (ans+1)/2;
}
int sub6()
{
	int A=0,B=0,res=0;
	for(int i=0,p=-1;i<=n;i++)
	{
		if(i<n&&s[i]==t[0])continue;
		int len=i-p-1;
		if(len<2)a[++A]=2-len;
		if(len>2)b[++B]=len-2;
		p=i;
	}
	sort(a+1,a+A+1,greater<int>());
	sort(b+1,b+B+1,greater<int>());
	for(int i=1,l=1,r=A;i<=B;i++)
	{
		while(l<=r&&b[i]>=2)b[i]-=a[l++],res++;
		if(b[i])
		{
			if(l>r)return -1;
			if(--a[r]==0)r--;
			res++;
		}
	}
	return res;
}
int solve()
{
	cin>>s>>t;
	n=s.size(),m=t.size();
	for(int i=0;i<n;i++)s[i]-='0';
	for(int i=0;i<m;i++)t[i]-='0';
	if(m==1)return sub1();
	if(m==2&&t[0]!=t[1])return sub2();
	if(m==2)return sub3();
	if(m==3&&t[0]!=t[2])return sub4();
	if(m==3&&t[0]!=t[1])return sub5();
	if(m==3)return sub6();
	return -2;
}
int main()
{
//	freopen("shin.in","r",stdin);
//	freopen("shin.out","w",stdout);
	ios::sync_with_stdio(false);
	cin.tie(NULL),cout.tie(NULL);
	int T=1;
	while(T--)printf("%d\n",solve());
	return 0;
}