# include <bits/stdc++.h>
using namespace std;
char s[200010],t[5];
int main()
{
	ios::sync_with_stdio(false);cin.tie(nullptr);
	cin>>s+1>>t+1;
	int n=strlen(s+1),m=strlen(t+1);
	auto flp=[&]()
	{
		for(int i=1;i<=n;i++) s[i]='0'+'1'-s[i];
		for(int i=1;i<=m;i++) t[i]='0'+'1'-t[i];
	};
	auto rev=[&]()
	{
		reverse(s+1,s+n+1);
		reverse(t+1,t+m+1);
	};
	if(m==1) cout<<(count_if(s+1,s+n+1,[](char c){return c==t[1];})?-1:0)<<"\n";
	else if(m==2)
	{
		if(t[1]==t[2])// 11
		{
			if(t[1]=='0') flp();
			int c0=(s[1]=='0')+(s[n]=='0'),c1=0;
			for(int i=1;i<n;i++)
				if(s[i]==s[i+1]) (s[i]=='0'?c0:c1)++;
			if(c1<=c0) cout<<c1<<"\n";
			else cout<<"-1\n";
		}
		else// 10
		{
			if(t[1]=='0') flp();
			int l=1,r=n,ans=0;
			while(l<=n && s[l]=='0') l++;
			while(r && s[r]=='1') r--;
			for(int i=l;i<r;i++) ans+=(s[i]=='1' && s[i+1]=='0');
			cout<<ans<<"\n";
		}
	}
	else
	{
		if(t[1]==t[2] && t[1]==t[3])// 111
		{
			if(t[1]=='0') flp();
			int c0=(s[1]=='0')+(s[n]=='0'),c1=0,ans=0;
			for(int i=1;i<n;i++) c0+=(s[i]=='0' && s[i+1]=='0');
			for(int i=1,j;i<=n;i=j)
				if(s[i]=='0') j=i+1;
				else
				{
					for(j=i;j<=n && s[j]=='1';j++);
					int cnt=j-i,mn=min(c0,(cnt-1)/2);
					ans+=mn;c0-=mn;cnt-=2*mn;
					c1+=(cnt==1);
					cnt=max(cnt-2,0);
					ans+=cnt;c1-=cnt;
				}
			cout<<(c1>=0?ans:-1)<<"\n";
		}
		else if(t[1]==t[3])// 010
		{
			if(t[1]=='1') flp();
			int l=1,r=n,cnt=0;
			while(l<=n && s[l]=='1') l++;
			while(r && s[r]=='1') r--;
			for(int i=l+1;i<r;i++) cnt+=(s[i-1]=='0' && s[i]=='1' && s[i+1]=='0');
			cout<<(cnt+1)/2<<"\n";
		}
		else// 110
		{
			if(t[2]==t[3]) rev();
			if(t[1]=='0') flp();
			int ans=0;
			for(int i=1;i<=n-2;i++) ans+=(s[i]=='1' && s[i+1]=='1' && s[i+2]=='0');
			cout<<ans<<"\n";
		}
	}
	return 0;
}