#include<bits/stdc++.h>
#define sqr(x) ((x)*(x))
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define ld long double
#define vi vector<int>
#define HEAP(...) priority_queue<__VA_ARGS__ >
#define heap(...) priority_queue<__VA_ARGS__,vector<__VA_ARGS__ >,greater<__VA_ARGS__ > > 
#define pii pair<int,int> 
#define pb push_back
#define mp make_pair
#define debuge cerr<<"isok"<<endl
#define debug(x) cerr<<#x<<"="<<x<<endl
#define dprintf(...) fprintf(stderr,__VA_ARGS__)
#define SS second
#define FF first
#define ls (k<<1)
#define rs (k<<1|1)
#define clr(a,x) memset(a,x,sizeof(a))
#define cpy(a,x) memcpy(a,x,sizeof(a))
#define file(x) freopen(x".in","r",stdin),freopen(x".out","w",stdout)
#define SZ(x) ((int)x.size())
using namespace std;
template<class T> inline void gmin(T &x,const T &y){if(x>y) x=y;}
template<class T> inline void gmax(T &x,const T &y){if(x<y) x=y;}
const int BufferSize=1<<16;
char buffer[BufferSize],*Bufferhead,*Buffertail;
bool Terminal;
inline char Getchar(){
	if(Bufferhead==Buffertail){
		int l=fread(buffer,1,BufferSize,stdin);
		if(!l){Terminal=1;return 0;}
		Buffertail=(Bufferhead=buffer)+l;
	}
	return *Bufferhead++;
}
template<class T>inline bool read(T &x){
	x=0;char c=Getchar(),rev=0;
	while(c<'0'||c>'9'){rev|=c=='-';c=Getchar();if(Terminal)return 0;}
	while(c>='0'&&c<='9') x=x*10+c-'0',c=Getchar();
	if(c=='.'){
		c=Getchar();double t=0.1;
		while(c>='0'&&c<='9') x=x+(c-'0')*t,c=Getchar(),t=t/10;
	}
	x=rev?-x:x;
	return 1;
}
template<class T1,class T2> inline bool read(T1 &x,T2 &y){return read(x)&read(y);}
template<class T1,class T2,class T3> inline bool read(T1 &x,T2 &y,T3 &z){return read(x)&read(y)&read(z);}
template<class T1,class T2,class T3,class T4> inline bool read(T1 &x,T2 &y,T3 &z,T4 &w){return read(x)&read(y)&read(z)&read(w);}
inline bool reads(char *x){
	char c=Getchar();
	while(c<33||c>126){c=Getchar();if(Terminal)return 0;}
	while(c>=33&&c<=126) (*x++)=c,c=Getchar();
	*x=0;return 1;
}
template<class T>inline void print(T x,const char c='\n'){
	if(!x){putchar('0');putchar(c);return;}
	if(x<0) putchar('-'),x=-x;
	int m=0,a[20];
	while(x) a[m++]=x%10,x/=10;
	while(m--) putchar(a[m]+'0');
	putchar(c);
}
//--------------------------------head---------------------------------------------

const int inf=0x3f3f3f3f;
const int N=1000005,M=100005,mod=1e9+7;
template<class T,class S> inline void ch(T &x,const S y){x=(x+y)%mod;}
inline int exp(int x,int y,const int mod=::mod){
	int ans=1;
	while(y){
		if(y&1) ans=(ll)ans*x%mod;
		x=(ll)x*x%mod;y>>=1;
	}return ans;
}

int n,ans,dp[N],mx[N];
char s1[N],s2[N],res[N];
vi now;

inline void solve(vi A){
	static int a[N],b[N];
	int m=A.size();
	gmax(ans,1);
	for(int i=1;i<=m;i++)
		a[i]=A[i-1];
	reverse(a+1,a+m+1);
//	for(int i=1;i<=m;i++)
//		printf("%d ",a[i]);puts("");
	a[m+1]=mx[a[m]]+1;m++;
	for(int i=1;i<=m;i++)
		b[i]=a[i]-i;
	for(int i=m-1,j=m;i;i--){
		int k=mx[a[i]]-i;//gmax(ans,lower_bound(b+1,b+m+1,mx[a[i]]-i
		while(j>1&&b[j-1]>=k) j--;
		gmax(ans,j-i);
	}
}

int main(){
#ifdef rqgao2014
	freopen("input.txt","r",stdin);
#endif
	scanf("%d",&n);
	scanf("%s%s",s1+1,s2+1);
	if(strcmp(s1+1,s2+1)==0){puts("0");return 0;}
	for(int i=n,j=n;i;i--){
		gmin(j,i);
		while(j&&s1[j]!=s2[i]) j--;
		if(!j){puts("-1");return 0;}
		gmax(mx[j],i);
	}
	int last=0;
	for(int i=n;i;i--){
		if(!mx[i]) continue;
//		dprintf("%d %d\n",i,mx[i]);
		if(last){
			if(mx[i]<last) solve(now),now.clear();
		}
		last=i;now.pb(i);
	}
	solve(now);
	for(int i=1;i<=mx[1];i++) res[i]=s1[1];
	printf("%d\n",ans);
	return 0;
}

Measured memory_bytes: 23788