Рифмовка

#include <iostream>
#include <vector>
#include <algorithm>
#include <tuple>

using namespace std;

vector<int> zfunc(const string& s){
    vector<int> z(s.size());
    int first = 0;
    int last = 1;
    for (int i = 1; i < s.size(); ++i){
        if (i >= first && i < last && z[i - first] + i < last){
            z[i] = z[i - first];
        } else {
            z[i] = max(0, last - i);
            first = i;
            while (s[i + z[i]] == s[z[i]] && i + z[i] < s.size()){
                ++z[i];
            }
            last = i + z[i];
        }
    }
    return z;
}

int main() {
    string s;
    cin >> s;
    reverse(s.begin(), s.end());
    vector<int> z = zfunc(s);
    vector<int> z_val(s.size(), 1);
    z_val[0] = 2;
    for (int i = 0; i < s.size(); ++i){
        ++z_val[z[i]];
    }
    for (int i = s.size() - 1; i >= 0; --i){
        if (z_val[i] > 1){
            cout << i;
            return 0;
        }
    }
    return 0;
};