#include<bits/stdc++.h>
using namespace std;
int main()
{
	string s; cin >> s;
	int mid = (s.size()-1)/2;
	cout << s[mid];
	for(int i = 1; i <= mid; i++)
		cout << s[mid+i] << s[mid-i];
	if(s.size() % 2 == 0) cout << s[s.size()-1] << endl;
	return 0;
}
 

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