#include <bits/stdc++.h>
using namespace std;
inline int getint() {
  int x;
  scanf("%d", &x);
  return x;
}
inline long long getlonglong() {
  long long x;
  scanf("%lld", &x);
  return x;
}
inline double getdouble() {
  double x;
  scanf("%lf", &x);
  return x;
}
int main() {
  int n;
  string s;
  cin >> n >> s;
  int t = 1;
  for (int i = 0; i < n; i += t) {
    cout << s[i];
    t++;
  }
  cout << endl;
  return 0;
}
