#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <math.h>
#include <string>
#include <algorithm>
using namespace std;
int main() {
int n;
string s;
cin >> n >> s;
int f = (sqrt(8 * n + 1) - 1) / 2;
for (int i = 1;i <= f;++i) {
int m = (i*(i + 1)) / 2;
cout << s[m - 1];
}
//system("pause");
return 0;
}