#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
const int inf = 1e9;
const long long INF = 1e18;
const double PI = acos(-1.0);
const double EPS = 1e-8;
const int MOD = 1000000007;
int main(int argc, char const *argv[]) {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  string s;
  cin >> s;
  s = " " + s;
  for (int i = 1; i <= 55; i++) {
    int len = i * (i + 1) / 2;
    if (len < s.size()) cout << s[len];
  }
  return 0;
}
