#include<bits/stdc++.h>

#define pb push_back
#define fi first
#define se second
#define mp make_pair

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef long double ld;

template <typename T> bool chkmin(T &x,T y){return x>y?x=y,1:0;}
template <typename T> bool chkmax(T &x,T y){return x<y?x=y,1:0;}

int readint(){
	int x=0,f=1; char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
	return x*f;
}

int n,m;
char s[200005],t[5];

int main(){
	scanf("%s%s",s+1,t+1);
	n=strlen(s+1);
	m=strlen(t+1);
	if(m==1){
		for(int i=1;i<=n;i++) if(s[i]==t[1]) return printf("-1\n"),0;
		printf("0\n");
		return 0;
	}
	if(m==2){
		if(t[1]==t[2]){
			int num=0;
			for(int i=1;i<=n;i++) if(s[i]==t[1]) num++;
			if(num>(n+1)/2) return printf("-1\n"),0;
			int ans=0;
			for(int i=2;i<=n;i++) ans+=s[i-1]==t[1]&&s[i]==t[1];
			printf("%d\n",ans);
		}
		else{
			s[0]=t[2],s[n+1]=t[1];
			int num=0;
			for(int i=1;i<=n+1;i++) if(s[i]!=s[i-1]) num++;
			printf("%d\n",num/2);
		}
		return 0;
	}
	return 0;
}