#include <bits/stdc++.h>
int main() {
  std::string s;
  std::cin >> s;
  int step = 1, ind = (s.size() - 1) / 2;
  for (int i = 0; i < s.size(); i++)
    std::cout << s[ind], ind += step, step += step / abs(step), step = -step;
  return 0;
}
