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

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

int main(void)
{
	scanf("%s%s",s+1,t+1);
	int n = strlen(s+1);
	int 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)
		{
			for(int i=1; i<=n; ++i)
				a[i] ^= 1;
			for(int i=1; i<=m; ++i)
				b[i] ^= 1;
		}
		
		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;
		}
	}
	return 0;
}