#include<bits/stdc++.h>

using namespace std;
const int maxn = 2e6 + 7;
const int SIGMA_SIZE = 128;
struct SuffixArray{
    int sa[maxn], S[maxn], rnk[maxn], tax[maxn], tp[maxn], height[maxn];
    int h[22][maxn];
    int n;
    int m = SIGMA_SIZE;
    void SA(string s) {
        int n = s.size();
        s = '#' + s;
        int m = SIGMA_SIZE;
        memset(tax,0,sizeof tax);
        auto RadixSort = [&]() {
            for (int i = 0; i <= m; ++i) tax[i] = 0;
            for (int i = 1; i <= n; ++i) ++tax[rnk[i]];
            for (int i = 1; i <= m; ++i) tax[i] += tax[i - 1];
            for (int i = n; i; --i) sa[tax[rnk[tp[i]]]--] = tp[i];
        };
        for (int i = 1; i <= n; ++i) {
            S[i] = s[i] - '0';
            tp[i] = i;
            rnk[i] = S[i];
        }
        RadixSort();
        for (int len = 1, p = 0; p != n; m = p, len <<= 1) {
            p = 0;
            for (int i = n - len + 1; i <= n; ++i) tp[++p] = i;
            for (int i = 1; i <= n; ++i) if (sa[i] > len) tp[++p] = sa[i] - len;
            RadixSort();
            std::swap(rnk, tp);
            p = 0;
            for (int i = 1; i <= n; ++i)
              rnk[sa[i]] = ((tp[sa[i]] == tp[sa[i-1]]) && (tp[sa[i] + len] == tp[sa[i-1] + len])) ? p : ++p;
        }
        for (int i = 1, p = 0; i <= n; ++i) {
            int pre = sa[rnk[i] - 1];
            if (p) --p;
            while (S[pre + p] == S[i + p]) ++p;
            h[0][rnk[i]] = height[rnk[i]] = p;
        }
        for (int i = 1; i <= 20; ++i) {
            memset(h[i], 0x3f, n * 4 + 4);
            for (int j = 1; j + (1 << i - 1) <= n; ++j)
                h[i][j] = min(h[i - 1][j], h[i - 1][j + (1 << i - 1)]);
        }
    }
    int Q(int l, int r) {
        if (l > r) swap(l, r);
        ++l;
        int k = __lg(r - l + 1);
        return min(h[k][l], h[k][r - (1 << k) + 1]);
    }
    int lcp(int i, int j) {
        if (i == j) return n - i + 1;
        return Q(rnk[i], rnk[j]);
    }
}sa;
int solve(int n,string s,string t) {
    string S = s,T = t;
    reverse(S.begin(),S.end());
    reverse(T.begin(),T.end());
    string tmp = s + '1' + '2' + S + '3' + t + T + '4';
    sa.SA(tmp);
    // cerr << tmp << endl;
    // cerr << s << "#\n";
    // cerr << "#" << t << "\n";
    // // 1 - n
    auto lcp = [&](int op1,int op2,int i,int j) {
        if(i > n || j > n || i < 1 || j < 1) return 0;
        if(op1) i += 2 * n;
        if(op2) j += 2 * n;
        int ans = sa.lcp(i,j);
        if(op1) ans = min(ans,3 * n - i + 1);
        else ans = min(ans,n - i + 1);
        if(op2) ans = min(ans,3 * n - j + 1);
        else ans = min(ans,n - j + 1);
        return ans;
    };
    auto lcs = [&](int op1,int op2,int i,int j) {
        if(i > n || j > n || i < 1 || j < 1) return 0;
        i = n - i + 1;
        j = n - j + 1;
        i += n;
        j += n;
        if(op1) i += 2 * n;
        if(op2) j += 2 * n;
        int ans = sa.lcp(i,j);
        if(op1) ans = min(ans,4 * n - i + 1);
        else ans = min(ans,2 * n - i + 1);
        if(op2) ans = min(ans,4 * n - j + 1);
        else ans = min(ans,2 * n - j + 1);
        return ans;
    };    
    int mx = 0;
    for(int x = 1;x <= n;x ++) {
        for(int y = 1;y + x - 1 <= n;y += x) {
            int l = y,r = y + x - 1;
            {
                int k = r + lcp(1,1,l,r + 1);
                int j = l - lcs(1,1,l - 1,r);
                int i = j - lcs(0,1,j - 1,j - 1 + x);
                if(k - i + 1 >= 2 * x) {
                    // cerr << x << " " << l << " " << r << endl;
                    mx = x;
                    break;
                }
            }
            {
                int t1 = lcp(0,1,l,r + 1);
                int k = t1 ? r + t1 + lcp(1,1,l + t1,r + t1 + 1) : r;
                int t2 = lcs(0,1,l - 1,r);
                int i = t2 ? l - t2 - lcs(0,0,l - t2 - 1,r - t2) : l;
                if(k - i + 1 >= 2 * x) {
                    // cerr << t1 << " " << t2 << endl;
                    // cerr << x << " " << l << " " << r << " " << i << " " << k << endl;
                    mx = x;
                    break;
                }
            }
        }
    }
    return mx;
    // return 0;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    n ++;
    string s,t,S,T;
    cin >> s >> t;
    S = s,T = t;
    reverse(S.begin(),S.end());
    reverse(T.begin(),T.end());
    // cout << solve(n,T,S) << endl;
    cout << max(solve(n,s,t),solve(n,T,S)) * 2 << "\n";
}
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