#include<bits/stdc++.h>
#define fi first
#define se second
#define eb emplace_back
#define mp make_pair
using namespace std;
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128;
template<typename T,typename U>
T ceil(T x, U y) {return (x>0?(x+y-1)/y:x/y);}
template<typename T,typename U>
T floor(T x, U y) {return (x>0?x/y:(x-y+1)/y);}
template<class T,class S>
bool chmax(T &a,const S b) {return (a<b?a=b,1:0);}
template<class T,class S>
bool chmin(T &a,const S b) {return (a>b?a=b,1:0);}
int popcnt(int x) {return __builtin_popcount(x);}
int popcnt(ll x) {return __builtin_popcountll(x);}
int topbit(int x) {return (x==0?-1:31-__builtin_clz(x));}
int topbit(ll x) {return (x==0?-1:63-__builtin_clzll(x));}
int lowbit(int x) {return (x==0?-1:__builtin_ctz(x));}
int lowbit(ll x) {return (x==0?-1:__builtin_ctzll(x));}

#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
typedef pair<int,int> pii; 
typedef vector<int> vi;
typedef vector<pii> vp;
typedef tuple<int,int,int> tiii;
int read() {
  int x=0,w=1; char c=getchar(); 
  while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
  while(isdigit(c)) {x=x*10+(c-'0'); c=getchar();}
  return x*w;
}

string s,t; int n;
char flip(char c) {
  if(c=='0') return '1';
  else return '0';
}
void solve0() {
  int cnt=0; rep(i,0,n-1) cnt+=(s[i]=='0');
  if(cnt) puts("-1"); else puts("0");
}
void solve00() {
  int cnt=0; rep(i,0,n-1) cnt+=(s[i]=='0');
  if(cnt>(n+1)/2) {puts("-1"); return;}
  cnt=0; rep(i,0,n-2) cnt+=(s[i]=='0'&&s[i+1]=='0');
  printf("%d\n",cnt);
}
void solve01() {
  int cnt=0; rep(i,1,n-1) cnt+=(s[i-1]=='0'&&s[i]=='1');
  printf("%d\n",cnt);
}
void solve000() {
  int cnt0=0,cnt1=0,cnt=0,ans=0,cur1=0,curo=0;
  rep(i,0,n-1) if(s[i]=='0') cnt0++; else cnt1++;
  if(cnt0>2*(cnt1+1)) {puts("-1"); return;}
  rep(i,0,n-1) if(s[i]=='0') {
    ++cnt;
    if(s[i+1]=='1'||i==n-1) {
      if(cnt==1) cur1++;
      else if(cnt&1) curo++;
      ans+=(cnt-1)/2; cnt=0;
    }
  }
  int cur=max(cur1-curo,0);
  int p=max(cur-(2*(cnt1+1)-cnt0),0);
  ans+=(p+1)/2; printf("%d\n",ans);
}
void solve010() { 
  int cnt=0;
  rep(i,1,n-2) if(s[i-1]=='0'&&s[i]=='1'&&s[i+1]=='0') cnt++;
  printf("%d\n",(cnt+1)/2);
}
void solve011() {
  static int f[200005]; int cnt=0,tot=0,ans=0;
  per(i,n-1,0) {
    if(s[i]=='1') ++cnt;
    else f[++tot]=cnt, cnt=0;
  }
  rep(i,1,tot) if(f[i]>1) ++ans;
  printf("%d\n",ans);
}

signed main() {
  cin>>s>>t; n=s.size();
  if(s.size()<t.size()) return puts("0"), 0;
  if(t=="0") {
    solve0();
  } else if(t=="1") {
    rep(i,0,n-1) s[i]=flip(s[i]);
    solve0();
  } else if(t=="00") {
    solve00();
  } else if(t=="01") {
    solve01();
  } else if(t=="10") {
    rep(i,0,n-1) s[i]=flip(s[i]);
    solve01();
  } else if(t=="11") {
    rep(i,0,n-1) s[i]=flip(s[i]);
    solve00();
  } else if(t=="000") {
    solve000();
  } else if(t=="001") {
    reverse(s.begin(),s.end());
    rep(i,0,n-1) s[i]=flip(s[i]);
    solve011();
  } else if(t=="010") {
    solve010();
  } else if(t=="011") {
    solve011();
  } else if(t=="100") {
    rep(i,0,n-1) s[i]=flip(s[i]);
    solve011();
  } else if(t=="101") {
    rep(i,0,n-1) s[i]=flip(s[i]);
    solve010();
  } else if(t=="110") {
    reverse(s.begin(),s.end());
    solve011();
  } else if(t=="111") {
    rep(i,0,n-1) s[i]=flip(s[i]);
    solve000();
  } else assert(0);
  return 0;
}