#include<bits/stdc++.h>
#define ll long long
#define ull unsigned ll
#define N 400005
using namespace std;
const ll mod=1e9+9;
ull pre[N],pw[N],suf[N];
char s[N],t[N],t1[N],t2[N];
int n;
int res;
int f[N];//longest HB
int ask(int l,int r,bool flag)//0up1down
{
	if(!flag) return pre[r]-pre[l-1]*pw[r-l+1];
	else return suf[l]-suf[r+1]*pw[r-l+1];
} 
void calc()
{
	pw[0]=1;
	for(int i=1;i<=n;i++) 
	{
		pw[i]=pw[i-1]*mod;
		pre[i]=pre[i-1]*mod+s[i];
	}
//	for(int i=1;i<=n;i++) cout<<s[i];cout<<"\n";
//	for(int i=1;i<=n;i++) cout<<t[i];cout<<"\n";
	for(int i=n;i>=1;i--)
		suf[i]=suf[i+1]*mod+s[i];
	for(int i=1;i<=n;i++)
	{
		int l=1,r=min(i,n-i+1);
		while(l<=r)
		{
			int mid=(l+r)/2;
			if(ask(i-mid+1,i,0)==ask(i,i+mid-1,1)) l=mid+1;
			else r=mid-1;
		}
		f[i]=l-1;
//		cout<<f[i]<<" ";
	}
//	cout<<"\n";
	for(int i=n;i>=1;i--)
		suf[i]=suf[i+1]*mod+t[i];
	for(int i=1;i<=n;i++)
	{
		int L=i-f[i],R=i+f[i];
		int l=1,r=min(L,n-R+1);
		while(l<=r)
		{
			int mid=(l+r)/2;
			if(ask(L-mid+1,L,0)==ask(R,R+mid-1,1)) l=mid+1;
			else r=mid-1;
		}
		res=max(res,l-1+f[i]-1);
	}
}
int main()
{
	scanf("%d",&n);
	scanf("%s%s",t1+1,t2+1);
	for(int i=1;i<=n;i++) s[i*2-1+1]=t1[i],s[i*2+1]='|';
	s[n*2+1+1]=t2[n];
	for(int i=1;i<=n;i++) t[i*2+1+1]=t2[i],t[i*2+1]='|';
	t[1+1]=t1[1];
	n=n*2+3;
	s[1]=t[1]=s[n]=t[n]='|';
	calc();
	swap(s,t);
	for(int i=1;i<=n/2;i++) swap(s[i],s[n-i+1]),swap(t[i],t[n-i+1]);
	calc();
	printf("%d",res);
	return 0;
}