#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  cin >> s;
  int n = s.size();
  vector<char> v;
  int cnt = 1, i = (n - 1) / 2;
  while (cnt <= n) {
    v.push_back(s[i]);
    if (cnt % 2 == 1)
      i += cnt;
    else
      i -= cnt;
    cnt++;
  }
  for (auto c : v) cout << c;
  cout << '\n';
  return 0;
}
