#include <bits/stdc++.h>
int main() {
  std::string t;
  std::cin >> t;
  std::string out = "";
  int start = (int)(round(((double)(t.size())) / 2)) - 1;
  out += t[start];
  for (int i = 1; i <= t.size(); i += 2) {
    start += i;
    if ((start >= 0) && (start < t.size())) {
      out += t[start];
    }
    start -= i + 1;
    if ((start >= 0) && (start < t.size())) {
      out += t[start];
    }
  }
  std::cout << out;
  return 0;
}
