#include <bits/stdc++.h>
#define re register
#define ull unsigned long long

using namespace std;

const int N = 2e5 + 10;
int n,ans;
ull base = 102401027,pw[N],h[2][2][N];
string tmp,s[2][2];

inline void init(){
    pw[0] = 1;
    for (re int i = 1;i <= n;i++) pw[i] = pw[i - 1] * base;
}

inline ull get(int ty,int op,int l,int r){
    // cerr << ty << " " << op << " " << l << " " << r << " " << h[ty][op][r] - h[ty][op][l - 1] * pw[r - l + 1] << " \n";
    return h[ty][op][r] - h[ty][op][l - 1] * pw[r - l + 1];
}

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    cin >> n; n += n + 1; init();
    for (re int ty = 0;ty <= 1;ty++){
        cin >> tmp;
        for (char c:tmp) s[ty][1] += '&',s[ty][1] += c; s[ty][1] += '&';
        s[ty][0] = s[ty][1]; reverse(s[ty][1].begin(),s[ty][1].end());
        for (re int op = 0;op <= 1;op++){
            s[ty][op] = ' ' + s[ty][op];
            for (re int i = 1;i <= n;i++) h[ty][op][i] = h[ty][op][i - 1] * base + s[ty][op][i];
        }
        // cerr << s[ty][0] << "\n";
    }
    // cerr << get(0,0,1,4) << " " << get(1,1,1,4) << " ???\n";
    for (re int i = 1;i <= n;i++){
        int len = 0,l = 0,r = min(i - 1,n - i);
        // cerr << l << " " << r << " range\n";
        while (l < r){
            int mid = l + r + 1 >> 1;
            // [i,i + mid] -> [n - i - mid + 1,n - i + 1]
            if (get(0,0,i - mid,i) == get(0,1,n - i - mid + 1,n - i + 1)) l = mid;
            else r = mid - 1;
        }
        if (s[0][0][i] == '&') len += l;
        else len += (l / 2) * 2 + 1;
        int L = i - l - 1,R = i + l - 1;
        // cerr << i << " " << l << " " << L << " " << R << " !!!\n";
        if (L < 1 || R > n || s[0][0][L] != s[1][0][R]) goto End1;
        l = 1,r = min(L,n - R + 1);
        while (l < r){
            int mid = l + r + 1 >> 1;
            // [R,R + mid - 1] -> [n - R - mid + 2,n - R + 1]
            // cerr << "[" << L - mid + 1 << "," << L << "] & [" << n - R - mid + 1 << "," << n - i + 1 << "] " << get(0,0,i - mid,i) << " " << get(0,1,n - i - mid + 1,n - i + 1) << " " << (get(0,0,i - mid,i) == get(0,1,n - i - mid + 1,n - i + 1)) << " check\n";
            if (get(0,0,L - mid + 1,L) == get(1,1,n - R - mid + 2,n - R + 1)) l = mid;
            else r = mid - 1;
        }
        len += l;
        End1:;
        // cerr << i << " " << len << " !!!\n";
        ans = max(ans,len);
    }
    for (re int i = 1;i <= n;i++){
        int len = 0,l = 0,r = min(i - 1,n - i);
        while (l < r){
            int mid = l + r + 1 >> 1;
            // [i,i + mid] -> [n - i - mid + 1,n - i + 1]
            if (get(1,0,i - mid,i) == get(1,1,n - i - mid + 1,n - i + 1)) l = mid;
            else r = mid - 1;
        }
        if (s[1][0][i] == '&') len += l;
        else len += (l / 2) * 2 + 1;
        int L = i - l + 1,R = i + l + 1;
        if (L < 1 || R > n || s[0][0][L] != s[1][0][R]) goto End2;
        l = 1,r = min(L,n - R + 1);
        while (l < r){
            int mid = l + r + 1 >> 1;
            // [R,R + mid - 1] -> [n - R - mid + 1,n - R + 2]
            if (get(0,0,L - mid + 1,L) == get(1,1,n - R - mid + 2,n - R + 1)) l = mid;
            else r = mid - 1;
        }
        len += l;
        End2:;
        ans = max(ans,len);
    }
    printf("%d",ans);
    return 0;
}