#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int MAXN = 2e5 + 5;

void flip(int *a,int n)
{
	for(int i=1; i<=n; ++i)
		a[i] ^= 1;
}

int n,m;
char s[MAXN], t[5];
int a[MAXN], b[5];

void rev_all(void)
{
	reverse(a+1, a+n+1);
	reverse(b+1, b+m+1);
}
void flip_all(void)
{
	flip(a,n);
	flip(b,m);
}

int main(void)
{
	scanf("%s%s",s+1,t+1);
	n = strlen(s+1);
	m = strlen(t+1);
	
	for(int i=1; i<=n; ++i)
		a[i] = s[i] - '0';
	for(int i=1; i<=m; ++i)
		b[i] = t[i] - '0';
	
	if(m == 1)
	{
		if(count(a+1, a+n+1, b[1]))
			printf("-1\n");
		else
			printf("0\n");
		return 0;
	}
	
	if(m == 2)
	{
		if(b[1] == 1)
			flip_all();
		
		if(b[2] == 1)
		{
			a[0] = 1; a[n+1] = 0;
			int ans = 0;
			for(int i=0,j=0; i<=n+1; i=j)
			{
				while(j<=n+1 && a[i] == a[j]) ++j;
				++ans;
			}
			printf("%d\n",ans / 2 - 1);
			return 0;
		}
		
		int cnt[2] = {0,0};
		for(int i=1; i<n; ++i)
		{
			if(a[i] == a[i+1])
				++cnt[a[i]];
		}
		
		if(cnt[0] > cnt[1])
			printf("-1\n");
		else
			printf("%d\n",cnt[0]);
		return 0;
	}
	
	if(b[1] != b[3])
	{
		if(b[2] == b[3]) rev_all();
		if(b[1] == 1) flip_all();
		
		while(n && a[n] == 0) --n;
		
		int ans = 0;
		for(int i=1,j=1; i<=n; i=j)
		{
			while(j<=n && a[i] == a[j]) ++j;
			if(a[i] == 0 && j-i >= 2) ++ans;
		}
		printf("%d\n",ans);
		return 0;
	}
	
	if(b[1] != b[2])
	{
		if(b[1]) flip_all();
		
		int ans = 0;
		for(int i=1,j=1; i<=n; i=j)
		{
			while(j<=n && a[i] == a[j]) ++j;
			if(i == 1 || j > n || a[i] == 0 || j-i > 1) continue;
			++ans;
		}
		printf("%d\n",(ans + 1) / 2);
		return 0;
	}
	
	if(b[1]) flip_all();
	
	int cnt = 0;
	a[0] = a[n+1] = 1;
	for(int i=0; i<=n; ++i)
		if(a[i] == 1 && a[i+1] == 1) ++cnt;
	
	int ans = 0;
	for(int i=1,j=1; i<=n; i=j)
	{
		while(j<=n && a[i] == a[j]) ++j;
		if(a[i] == 1) continue;
		if(j-i < 3) continue;
		
		int rem = j-i;
		while(rem >= 3) rem -= 2, ++ans;
	}
	
	if(ans > cnt)
		printf("%d\n",-1);
	else
		printf("%d\n",ans);
	return 0;
}