第二个测试点没过...

#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;
int main()
{
	string a;
	long long n, t = 0;
	cin >> a;
	cin >> n;
	long long len = a.size(), cnt = log10((n - 1) / len) / log10(2);
	while (n > len)
	{
		long long temp = n;
		n = n - pow(2, cnt) * len - 1;
		if (n <= 0)n = temp - 1;
		cnt = log10((n - 1) / len) / log10(2);
	}
	cout << a[n - 1];
}

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