Envío 2061

Código

#include <iostream>
#include <string>

using namespace std;

int main() {
  string input;
  cin >> input;
  int max_border = 0;
  for (int i = 1; i < input.length(); i++) {
	 string left = input.substr(0, i);
	 int rightStart = input.length() - left.length();
	 string right = input.substr(rightStart);
	 if(left == right) {
		max_border = left.length();
	 }
  }
  cout << max_border << endl;
  return 0;
}