#include <bits/stdc++.h>
template <std::uint64_t a, std::uint64_t b>
struct hs {
    std::vector<std::uint64_t> h, hr, p;
    hs(const std::string &s) : h(s.size()), hr(s.size()), p(s.size() + 1) {
        p[0] = 1;
        for (int i = 1; i < p.size(); ++i)
            p[i] = p[i - 1] * a % b;
        for (int i = 0; i < s.size(); ++i)
            h[i] = ((i ? h[i - 1] : 0) * a + s[i]) % b;
        for (int i = s.size(); i--;)
            hr[i] = ((i + 1 < s.size() ? hr[i + 1] : 0) * a + s[i]) % b;
    }
    std::uint64_t get(int l, int r) const { return (h[r] - (l ? h[l - 1] : 0) * p[r - l + 1] % b + b) % b; }
    std::uint64_t getr(int l, int r) const { return (hr[l] - (r + 1 < hr.size() ? hr[r + 1] : 0) * p[r - l + 1] % b + b) % b; }
};
int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.tie(nullptr);
    int n;
    std::string s1, s2;
    std::cin >> n >> s1 >> s2;
    hs<131, 998244353> h1(s1), h2(s2);
    int ans = 0;
    for (int i = 0; i < n; ++i) {
        int l = 0, r = std::min(i + 1, n - i);
        while (l < r) {
            int mid = (l + r + 1) >> 1;
            if (h1.get(i - mid + 1, i) == h1.getr(i, i + mid - 1))
                l = mid;
            else
                r = mid - 1;
        }
        int k = l;
        r = std::min(i + 1, n - i + 1);
        while (l < r) {
            int mid = (l + r + 1) >> 1;
            if (h1.get(i - mid + 1, i - k) == h2.getr(i + k - 1, i + mid - 2))
                l = mid;
            else
                r = mid - 1;
        }
        ans = std::max(ans, l * 2 - 1);
    }
    for (int i = 0; i < n; ++i) {
        int l = 0, r = std::min(i + 1, n - i);
        while (l < r) {
            int mid = (l + r + 1) >> 1;
            if (h2.get(i - mid + 1, i) == h2.getr(i, i + mid - 1))
                l = mid;
            else
                r = mid - 1;
        }
        int k = l;
        r = std::min(i + 2, n - i);
        while (l < r) {
            int mid = (l + r + 1) >> 1;
            if (h1.get(i - mid + 2, i - k + 1) == h2.getr(i + k, i + mid - 1))
                l = mid;
            else
                r = mid - 1;
        }
        ans = std::max(ans, l * 2 - 1);
    }
    for (int i = 0; i + 1 < n; ++i) {
        if (s1[i] == s1[i + 1]) {
            int l = 0, r = std::min(i + 1, n - i - 1);
            while (l < r) {
                int mid = (l + r + 1) >> 1;
                if (h1.get(i - mid + 1, i) == h1.getr(i + 1, i + 1 + mid - 1))
                    l = mid;
                else
                    r = mid - 1;
            }
            int k = l;
            r = std::min(i + 1, n - i - 1 + 1);
            while (l < r) {
                int mid = (l + r + 1) >> 1;
                if (h1.get(i - mid + 1, i - k) == h2.getr(i + 1 + k - 1, i + 1 + mid - 2))
                    l = mid;
                else
                    r = mid - 1;
            }
            ans = std::max(ans, l * 2);
        }
    }
    for (int i = 0; i + 1 < n; ++i) {
        if (s2[i] == s2[i + 1]) {
            int l = 0, r = std::min(i + 1, n - i - 1);
            while (l < r) {
                int mid = (l + r + 1) >> 1;
                if (h2.get(i - mid + 1, i) == h2.getr(i + 1, i + 1 + mid - 1))
                    l = mid;
                else
                    r = mid - 1;
            }
            int k = l;
            r = std::min(i + 2, n - i - 1);
            while (l < r) {
                int mid = (l + r + 1) >> 1;
                if (h1.get(i - mid + 2, i - k + 1) == h2.getr(i + 1 + k, i + 1 + mid - 1))
                    l = mid;
                else
                    r = mid - 1;
            }
            ans = std::max(ans, l * 2);
        }
    }
    for (int i = 0; i < n; ++i) {
        if (s1[i] == s2[i]) {
            int l = 0, r = std::min(i + 1, n - i);
            while (l < r) {
                int mid = (l + r + 1) >> 1;
                if (h1.get(i - mid + 1, i) == h2.getr(i, i + mid - 1))
                    l = mid;
                else
                    r = mid - 1;
            }
            ans = std::max(ans, l * 2);
        }
    }
    std::cout << ans << '\n';
    return 0;
}