#include<bits/stdc++.h>
using namespace std;
#define N 200005
#define ull unsigned long long
int n,out;
char cc[2][N],c[2][N];
ull bs=131,p[2][N],s[2][N],pw[N];
inline ull chk(int c,int l,int r,int op){
    if(op==1) return p[c][r]-p[c][l-1]*pw[r-l+1];
    return s[c][l]-s[c][r+1]*pw[r-l+1];
}
int main(){
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    cin>>n;
    cin>>(cc[0]+1)>>(cc[1]+1);
    n=2*n+2;
    for(int j=1;j<=n;++j) c[0][j+1]=j&1?cc[0][(j+1)/2]:'#';
    for(int j=1;j<=n;++j) c[1][j+2]=j&1?cc[1][(j+1)/2]:'#';
    c[0][1]=c[1][1]=c[1][2]=c[0][n]='#';
    pw[0]=1;
    for(int i=1;i<=n;++i) pw[i]=pw[i-1]*bs;
    for(int i=0;i<2;++i) for(int j=1;j<=n;++j) p[i][j]=p[i][j-1]*bs+c[i][j];
    for(int i=0;i<2;++i) for(int j=n;j>=1;--j) s[i][j]=s[i][j+1]*bs+c[i][j];
    for(int i=1,l,r,mid,ans,p,q,ta;i<=n;++i){
        l=1,r=min(i,n-i+1),ans=0;
        while(l<=r){
            mid=(l+r)>>1;
            if(chk(0,i-mid+1,i,0)==chk(1,i,i+mid-1,1)) l=mid+1,ans=mid;
            else r=mid-1;
        }
        out=max(out,ans);
        l=1,r=min(i,n-i+1),ans=0;
        while(l<=r){
            mid=(l+r)>>1;
            if(chk(0,i-mid+1,i,0)==chk(0,i,i+mid-1,1)) l=mid+1,ans=mid;
            else r=mid-1;
        }
        p=i-ans,q=i+ans-1,ta=ans;
        l=1,r=min(p,n-q+1),ans=0;
        while(l<=r){
            mid=(l+r)>>1;
            if(chk(0,p-mid+1,p,0)==chk(1,q,q+mid-1,1)) l=mid+1,ans=mid;
            else r=mid-1;
        }
        out=max(out,ta+ans);
        l=1,r=min(i,n-i+1),ans=0;
        while(l<=r){
            mid=(l+r)>>1;
            if(chk(1,i-mid+1,i,0)==chk(1,i,i+mid-1,1)) l=mid+1,ans=mid;
            else r=mid-1;
        }
        p=i-ans+1,q=i+ans,ta=ans;
        l=1,r=min(p,n-q+1),ans=0;
        while(l<=r){
            mid=(l+r)>>1;
            if(chk(0,p-mid+1,p,0)==chk(1,q,q+mid-1,1)) l=mid+1,ans=mid;
            else r=mid-1;
        }
        out=max(out,ta+ans);
    }
    cout<<out-1;
}