/*

_/      _/       _/_/_/      _/      _/    _/           _/_/_/_/_/
 _/    _/      _/      _/     _/    _/     _/           _/
  _/  _/      _/               _/  _/      _/           _/
   _/_/       _/                 _/        _/           _/_/_/_/
  _/  _/      _/                 _/        _/           _/
 _/    _/      _/      _/        _/        _/           _/
_/      _/       _/_/_/          _/        _/_/_/_/_/   _/_/_/_/_/

*/
#include <bits/stdc++.h>
#define ll long long
#define lc(x) ((x) << 1)
#define rc(x) ((x) << 1 | 1)
#define ru(i, l, r) for (int i = (l); i <= (r); i++)
#define rd(i, r, l) for (int i = (r); i >= (l); i--)
#define mid ((l + r) >> 1)
#define pii pair<int, int>
#define mp make_pair
#define fi first
#define se second
#define sz(s) (int)s.size()
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
using namespace std;
mt19937 Rand(chrono::steady_clock::now().time_since_epoch().count());
int read() {
    int x = 0, w = 0; char ch = getchar();
    while(!isdigit(ch)) w |= ch == '-', ch = getchar();
    while(isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
    return w ? -x : x;
}
char s[200005], t[10];
int main() {
    scanf("%s%s", s + 1, t + 1);
    int n = strlen(s + 1), m = strlen(t + 1);
    if(t[1] == '1') {
    	ru(i, 1, n) s[i] = '0' + '1' - s[i];
    	ru(i, 1, m) t[i] = '0' + '1' - t[i];
    }
    if(m == 1) {
    	int fl = 1;
    	ru(i, 1, n) fl &= s[i] != '0';
    	printf("%d\n", fl - 1);
    }
    if(m == 2) {
    	if(t[2] == '0') {
    		int sum = 0;
    		ru(i, 1, n) sum += (s[i] == '0') - (s[i] == '1');
    		if(sum <= 1) {
    			int cnt = 0;
    			ru(i, 1, n - 1) cnt += s[i] == '0' && s[i + 1] == '0';
    			printf("%d\n", cnt);
    		}
    		else printf("-1\n");
    	}
    	else {
    		int cnt = 0;
    		ru(i, 1, n - 1) cnt += s[i] == '0' && s[i + 1] == '1';
    		printf("%d\n", cnt);
    	}
    }
    if(m == 3) {
    	if(t[2] == '0' && t[3] == '0') {
    		int sum = 0;
    		ru(i, 1, n) sum += (s[i] == '0') - 2 * (s[i] == '1');
    		if(sum <= 2) {
    			int las = 1, cnt = 0, cnt2 = 0, cnt0 = 0;
    			s[n + 1] = '1';
    			ru(i, 1, n + 1) if(s[i] == '1') {
					if(las < i) cnt += (i - las - 1) / 2, cnt2 += (i - las - 2) / 2;
					else cnt0++;
					las = i + 1;
				}
				printf("%d\n", cnt + max(0, cnt2 - cnt0));
    		}
    		else printf("-1\n");
    	}
    	if(t[2] == '1' && t[3] == '1') {
    		reverse(s + 1, s + n + 1);
    		ru(i, 1, n) s[i] = '0' + '1' - s[i];
    		t[2] = '0';
    	}
    	if(t[2] == '0' && t[3] == '1') {
    		int cnt = 0;
    		ru(i, 1, n - 2) if(s[i] == '0' && s[i + 1] == '0' && s[i + 2] == '1') cnt++;
    		printf("%d\n", cnt);
    	}
    	if(t[2] == '1' && t[3] == '0') {
    		int cnt = 0;
    		ru(i, 1, n - 2) if(s[i] == '0' && s[i + 1] == '1' && s[i + 2] == '0') cnt++;
    		printf("%d\n", (cnt + 1) / 2);
    	}
    }
    return 0;
}