#include <bits/stdc++.h>
using namespace std;
template <typename T>
void read_vector(vector<T>& v) {
  for (T& el : v) cin >> el;
}
template <typename T>
void min_self(T& a, T& b) {
  a = min(a, b);
};
template <typename T>
void max_self(T& a, T& b) {
  a = max(a, b);
};
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N, k = 0;
  cin >> N;
  string S;
  cin >> S;
  string ans;
  for (int i = 0; i < N; i += (k + 1)) {
    ans += S[i];
    k++;
  }
  cout << ans << "\n";
  return 0;
}
