#include<bits/stdc++.h>
#define LL long long
#define LLL __int128
#define uint unsigned
#define ldb long double
#define uLL unsigned long long
using namespace std;
int plen,ptop,pstk[40];
char rdc[1<<20],out[1<<20],*rS,*rT;
#define gc() (rS==rT?rT=(rS=rdc)+fread(rdc,1,1<<20,stdin),(rS==rT?EOF:*rS++):*rS++)
#define pc(x) out[plen++]=(x)
#define flush() fwrite(out,1,plen,stdout),plen=0
template<class T=int>inline T read(){
    T x=0;char ch;bool f=1;
    while(!isdigit(ch=gc()))if(ch=='-')f^=1;
    do x=(x<<1)+(x<<3)+(ch^48);while(isdigit(ch=gc()));
    return (f)?(x):(-x);
}
inline int read(char*const s){
	char *t=s,ch;
    while(!isgraph(ch=gc()));
	do (*(t++))=ch;while(isgraph(ch=gc()));
	return (*t)='\000',t-s;
}
template<class T=int>inline void write(T x){
	if(plen>=1000000)flush();
	if(!x)return pc('0'),void();
	if(x<0)pc('-'),x=-x;
	for(;x;x/=10)pstk[++ptop]=x%10;
	while(ptop)pc(pstk[ptop--]+'0');
}
inline void write(const char*s){
	if(plen>=1000000)flush();
	for(int i=0;(*(s+i))!='\000';pc(*(s+(i++))));
}
inline void write(char*const s){
	if(plen>=1000000)flush();
	for(int i=0;(*(s+i))!='\000';pc(*(s+(i++))));
}
typedef pair<LL,LL> PII;
const int N=2e5+5;
int n,m,q;
char s[N],t[10];
struct node{char x;int l,r;}T[N];
inline int A(char a){
	for(int i=1;i<=n;++i)if(s[i]==a)return -1;
	return 0;
}
inline int AA(char a){
	int cnt=0;
	for(int i=1;i<=n;++i)if(s[i]==a)++cnt;
	if((n-cnt)<n/2)return -1;
	int ans=0;
	for(int i=1;i<=q;++i)
		if(T[i].x==a)ans+=T[i].r-T[i].l;
	return ans;
}
inline int AB(char a,char b){
	int ans=0;
	for(int i=2;i<=q;++i)
		if(T[i].x==b)++ans;
	return ans;
}
inline int AAA(char a){
	int cnt=0;
	for(int i=1;i<=n;++i)if(s[i]==a)++cnt;
	if((n-cnt)<n/3)return -1;
	int ans=0;
	priority_queue<int>Q1,Q2;
	for(int i=1;i<=q;++i)
		if(T[i].x!=a)for(int j=1;j<=T[i].r-T[i].l;++j)Q1.push(2);
		else if(T[i].l==T[i].r)Q1.push(1);
		else if(T[i].r-T[i].l>1)Q2.push(T[i].r-T[i].l-1);
	if(s[1]!=a)Q1.push(2);
	if(s[n]!=a)Q1.push(2);
	for(;!Q1.empty()&&!Q2.empty();){
		int x=Q1.top(),y=Q2.top(),z=min(x,y);
		Q1.pop(),Q2.pop(),++ans;
		if(x>z)Q1.push(x-z);
		if(y>z)Q2.push(y-z);
	}
	return ans;
}
inline int ABA(char a,char b){
	int ans=1;
	for(int i=2;i<q;++i)
		if(T[i].x==b&&T[i].l==T[i].r)++ans;
	return ans/2;
}
inline int AXB(char a,char x,char b){
	int ans=0;
	for(int i=3;i<=n;++i)
		ans+=(s[i-2]==a&&s[i-2]==x&&s[i]==b);
	return ans;
}
inline void MAIN(){
	n=read(s+1),m=read(t+1),q=0;
	for(int i=2,j=1;i<=n+1;++i)if(s[i]!=s[j])T[++q]=(node){s[j],j,i-1},j=i;
	if(m==1)write(A(t[1])),pc('\n');
	else if(m==2)write(t[1]==t[2]?AA(t[1]):AB(t[1],t[2])),pc('\n');
	else if(t[1]==t[2]&&t[1]==t[3])write(AAA(t[1])),pc('\n');
	else write(t[1]==t[3]?ABA(t[1],t[2]):AXB(t[1],t[2],t[3])),pc('\n');
}
signed main(){
	for(int T=1;T--;MAIN());
	return flush(),0;
}
/*

*/