#include <bits/stdc++.h>
using namespace std;
#define _ <<" "<<
#define sz(x) ((int) (x).size())
typedef pair<int, int> pii;
typedef long long ll;
const int maxn = 1e6 + 5;


int n, m;
char A[maxn], B[maxn];
int f[maxn][85];
pii pre[maxn][85];

int main() {
    // freopen("a.out", "w", stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin >> n;
    for (int i = 1;i <= n; ++i) cin >> A[i];
    for (int i = 1;i <= n; ++i) cin >> B[i];
    // if (n < 5000) {
    if (false) {
        vector<vector<int>> dp(n+1,vector<int>(n+1));
        vector<vector<pii>> pre1(n+1,vector<pii>(n+1));
        for (int i = 1;i <= n; ++i) {
            for (int j = 1;j <= n;++j) {
                if (A[i] == B[j]) dp[i][j] = dp[i-1][j-1] + 1, pre1[i][j] = {i-1,j-1};
                if (dp[i][j-1] > dp[i][j]) {
                    dp[i][j] = dp[i][j-1];
                    pre1[i][j] = {i, j - 1};
                }
                if (dp[i-1][j] > dp[i][j]) {
                    dp[i][j] = dp[i-1][j];
                    pre1[i][j] = {i - 1, j};
                }
            }
        }
        cout << dp[n][n] << endl;
        int x = n, y = n;
        vector<char> ans;
        while (sz(ans) < n/2) {
            auto [nx,ny] = pre1[x][y];
            if (nx == x-1 && ny == y-1) {
                ans.push_back(A[x]);
            } 
            x = nx; y = ny;
        }
        for (int i = sz(ans)-1;i >= 0; --i) cout << ans[i];
        cout << '\n';
        return 0;
    }
    
    int base = 40;
    f[0][base] = 0;
    for (int i = 1;i <= n; ++i) {
        for (int j = 39;j >= -39; --j) if (i-j >= 1 && i-j <= n) {
            if (A[i] == B[i-j]) {
                f[i][j+base] = f[i-1][j+base] + 1;
                pre[i][j+base] = {i-1, j+base};
            }
            if (f[i][j+base] < f[i-1][j-1+base]) {
                f[i][j+base] = f[i-1][j-1+base];
                pre[i][j+base] = {i-1,j-1+base};
            }
            if (f[i][j+base] < f[i][j+1+base]) {
                f[i][j+base] = f[i][j+1+base];
                pre[i][j+base] = {i, j+1+base};
            }
        }
    }
    int x = n, y = base;
    int cnt = 0;
    // cout << f[n][base] << endl;
    vector<char> ans;
    while (cnt < n / 2 && x > 0) {
        auto [nx,ny] = pre[x][y];
        // cout << x _ nx _ (y-base + x) _ (ny-base + nx) _ f[x][y] << endl;
        if (nx == x-1 && ny == y) {
            ans.push_back(A[x]);
            cnt++;
        }
        x = nx; y = ny;
    }
    for (int i = sz(ans)-1;i >= 0; --i) cout << ans[i];
    cout << '\n';
    return 0;
}