#include <bits/stdc++.h>
using namespace std;

const int N = 5e5 + 5;

int n, ans, lg[N];
string s, t;

struct SA {
	int m, p, a[N], rk[N], sa[N], cnt[N], id[N], nrk[N], ht[N], f[N][20];

	void work(string s) {
		m = s.size();
		for (int i = 1; i <= m; i++) {
			a[i] = s[i];
		}
		for (int i = 1; i <= 127; i++) {
			cnt[i] = 0;
		}
		for (int i = 1; i <= m; i++) {
			cnt[a[i]]++;
		}
		for (int i = 1; i <= 127; i++) {
			cnt[i] += cnt[i - 1];
		}
		for (int i = 1; i <= m; i++) {
			sa[cnt[a[i]]--] = i;
		}
		p = 0;
		for (int i = 1; i <= m; i++) {
			rk[sa[i]] = a[sa[i]] == a[sa[i - 1]] ? p : ++p;
		}
		for (int w = 1; ; w <<= 1) {
			for (int i = 1; i <= p; i++) {
				cnt[i] = 0;
			}
			for (int i = 1; i <= m; i++) {
				cnt[rk[i]]++;
			}
			for (int i = 1; i <= p; i++) {
				cnt[i] += cnt[i - 1];
			}
			p = 0;
			for (int i = 0; i < w; i++) {
				id[++p] = m - i;
			}
			for (int i = 1; i <= m; i++) {
				if (sa[i] > w) {
					id[++p] = sa[i] - w;
				}
			}
			for (int i = p; i >= 1; i--) {
				sa[cnt[rk[id[i]]]--] = id[i];
			}
			p = 0;
			for (int i = 1; i <= m; i++) {
				nrk[sa[i]] = rk[sa[i]] == rk[sa[i - 1]] && rk[sa[i] + w] == rk[sa[i - 1] + w] ? p : ++p;
			}
			for (int i = 1; i <= m; i++) {
				rk[i] = nrk[i];
			}
			if (p == m) {
				break;
			}
		}
		for (int i = 1, k = 0; i <= m; i++) {
			if (k) {
				k--;
			}
			while (a[i + k] == a[sa[rk[i] - 1] + k]) {
				k++;
			}
			ht[rk[i]] = k;
		}
		for (int i = 1; i <= m; i++) {
			f[i][0] = ht[i];
		}
		for (int j = 1; 1 << j <= m; j++) {
			for (int i = 1; i + (1 << j) - 1 <= m; i++) {
				f[i][j] = min(f[i][j - 1], f[i + (1 << j - 1)][j - 1]);
			}
		}
	}

	int query(int i, int j) {
		int k = lg[j - i + 1];
		return min(f[i][k], f[j - (1 << k) + 1][k]);
	}

	int lcp(int i, int j) {
		int x = rk[i], y = rk[j];
		if (x > y) {
			swap(x, y);
		}
		return query(x + 1, y);
	}
} S, T;

int main() {
	// freopen("d.in", "r", stdin);
	// freopen("d.out", "w", stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);
	for (int i = 2; i <= N - 5; i++) {
		lg[i] = lg[i / 2] + 1;
	}
	cin >> n >> s >> t;
	n++;
	s = s + t.back();
	t = s.front() + t;
	S.work('A' + s + 'B' + t + 'C');
	reverse(s.begin(), s.end());
	reverse(t.begin(), t.end());
	T.work('A' + s + 'B' + t + 'C');
	reverse(s.begin(), s.end());
	reverse(t.begin(), t.end());
	for (int len = n / 2; len >= 1; len--) {
		for (int i = len * 2; i <= n; i += len) {
			int j = i - len;
			if (T.lcp(n - j + 1, n - i + 1) + S.lcp(j + 1, i + 1) >= len || T.lcp(n + 1 + n - j + 1, n + 1 + n - i + 1) + 
				S.lcp(n + 1 + j + 1, n + 1 + i + 1) >= len || T.lcp(n - j + 1, n + 1 + n - i + 1) + 
				S.lcp(j + 1, n + 1 + i + 1) >= len) {
				ans = max(ans, len);
				break;
			} else {
				int s = T.lcp(n - j + 1, n + 1 + n - i + 1);
				int p = S.lcp(j + 1, n + 1 + i + 1);
				if (j - s >= 1 && T.lcp(n - (j - s) + 1, n - (i - s) + 1) >= len - s - p) {
					ans = max(ans, len);
					break;
				}
				if (i + 1 + p <= n && S.lcp(n + 1 + j + 1 + p, n + 1 + i + 1 + p) >= len - s - p) {
					ans = max(ans, len);
					break;
				}
				s = T.lcp(n + 1 + n - j + 1, n + 1 + n - i + 1);
				p = S.lcp(n + 1 + j + 1, n + 1 + i + 1);
				if (j - s >= 1 && T.lcp(n - (j - s) + 1, n + 1 + n - (i - s) + 1) >= len - s - p) {
					ans = max(ans, len);
					break;
				}
				s = T.lcp(n - j + 1, n - i + 1);
				p = S.lcp(j + 1, i + 1);
				if (i + 1 + p <= n && S.lcp(j + p + 1, n + 1 + i + p + 1) >= len - s - p) {
					ans = max(ans, len);
					break;
				}
			}
		}
	}
	cout << ans * 2 << '\n';

	return 0;
}