#include<iostream>
#include<cstring>
#include<algorithm>
#include<vector>
#include<set>
#include<cstdlib>
using namespace std;
const int maxn=200005;
int n,m,p[2];
char str[maxn],t[5];
signed main(){
	ios::sync_with_stdio(false);cin.tie(0);
	cin>>str+1>>t+1;
	n=strlen(str+1);m=strlen(t+1);
	if(t[1]=='1'){
		for(int i=1;i<=n;++i)str[i]='0'+'1'-str[i];
		for(int i=1;i<=m;++i)t[i]='0'+'1'-t[i];
	}
	int fg=1;
	for(int i=0;i<=n-m;++i){
		int tmp=1;
		for(int j=1;j<=m;++j)if(str[i+j]!=t[j]){
			tmp=0;
			break;
		}
		if(tmp){
			fg=0;
			break;
		}
	}
	if(fg){
		cout<<'0';
		return 0;
	}
	if(m==1){
		cout<<"-1";
		return 0;
	}
	if(m==2){
		if(t[2]=='0'){
			int num=0;
			for(int i=1;i<=n;++i)if(str[i]=='0')++num;
			if(num>(n+1)/2)cout<<"-1";
			else{
				num=0;
				for(int i=1;i<n;++i)if(str[i]=='0'&&str[i+1]=='0')++num;
				cout<<num;
			}
		}
		else{
			int num=0;
			for(int i=2;i<=n;++i)if(str[i-1]=='0'&&str[i]=='1')++num;
			cout<<num;
		}
		return 0;
	}
	if(t[2]=='0'&&t[3]=='0'){
		int num=0;
		for(int i=1;i<=n;++i)if(str[i]=='0')++num;
		if(num>n-n/3)cout<<"-1";
		else{
			num=0;
			for(int i=1,j=0;i<=n+1;++i){
				if(i==n+1||str[i]=='1'){
					if(j){
						num+=(j-i-1)/2;
						j=0;
					}
				}
				else if(!j)j=i;
			}
			cout<<num;
		}
	}
	else if(t[3]=='1'){
		if(t[2]=='0'){
			reverse(str+1,str+n+1);
			for(int i=1;i<=n;++i)str[i]='0'+'1'-str[i];
		}
		int ans=0;
		for(int i=1,j=0;i<=n+1;++i){
			if(i==n+1||str[i]=='0'){
				if(j){
					if(i-j>1&&j>1)ans++;
					j=0;
				}
			}
			else if(!j)j=i;
		}
		cout<<ans;
	}
	else{
		int ans=0;
		for(int i=2;i<n;++i)if(str[i-1]=='0'&&str[i]=='1'&&str[i+1]=='0')++ans;
		cout<<(ans+1)/2;
	}
	return 0;
}