PALIN

#include <bits/stdc++.h>
#define sz size
#define pb push_back
using namespace std;

int n; string s;
int f[5005][5005];

void dp() {
    for (int k = 1; k <= n; k++)
    for (int i = 1; i <= n - k + 1; i++) {
        int j = i + k - 1;
        if (s[i] == s[j]) f[i][j] = f[i + 1][j - 1];
        else f[i][j] = min(f[i + 1][j], f[i][j - 1]) + 1;
    }
    cout << f[1][n] << '\n';
}

void tb() {
    vector<char> l, r;
    int i = 1, j = n;
    while (i <= j) {
        if (s[i] == s[j]) {
            l.pb(s[i]);
            if (i != j) r.pb(s[j]);
            i++; j--;
        } else {
            if (f[i + 1][j] < f[i][j - 1]) {
                l.pb(s[i]); r.pb(s[i]);
                i++;
            } else {
                l.pb(s[j]); r.pb(s[j]);
                j--;
            }
        }
    }
    for (int i = 0; i < (int)l.sz(); i++) cout << l[i];
    for (int i = r.sz() - 1; i >= 0; i--) cout << r[i];
    cout << '\n';
}

int main() {
    cin >> n;
    cin >> s;
    s = '$' + s;
    dp(); tb();
}