Z-1

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

const int N = 111;
string s;
char ans[N];
int f[N][N],a[N];


int rec(int l,int r) {
    if (l > r) return 0;
    if (!f[l][r])
        if (s[l]==s[r]) f[l][r] = rec(l + 1, r - 1) + 2 - (l == r);
        else f[l][r] = max(rec(l + 1, r), rec(l, r - 1));
    return f[l][r];
}
void print(int l, int r, int L, int R) {
    while (l <= r) {
        if (l == r && f[l][r] == 1) {
            ans[L] = s[l];
            ++L;
            ++l;
        } else if (s[l] == s[r]) {
            ans[L] = s[l];
            ++L;
            ++l;
            ans[R] = s[r];
            --r;
            --R;
        } else {
            if (f[l + 1][r] > f[l][r - 1]) ++l;
            else r--;
        }
    }
}

int main(){
    ifstream fin("input.txt");
    ofstream fout("output.txt");
    fin >> s;
    int n = s.length();
    rec(0, n - 1);
    print(0, n - 1, 0, f[0][n - 1] - 1);
    fout << f[0][n - 1] << endl << ans;
    return 0;
}