样例可以过，不知道错哪了，dalao们，帮帮我

#include <bits/stdc++.h>
using namespace std ;	
string s ;
int ll ;
int f ;
int ans ;
void cow ( long long , long long ) ;
int main ( ){
	long long n ;
	cin >> s ;
	cin >> n ;
	int l = s.size ( ) ;
	ll = l ;
	int cnt = 1 ;
	if  ( n <= l ){
		cout << s[n-1] ;
		return 0 ;
	}
	for ( int i = 1 ; ; ++i ){
			if ( l * 2 < n ){
				cnt ++;
				l*=2;
			}else {
				cnt++;
				l *= 2 ;
				break ;	
			}	
	}
	cow ( n , l );
	cout << s[ans-1];
	return 0 ;
}
void cow ( long long n , long long  l ){
	if ( n <= ll ) {
		//cout << "return " ;
		ans = n ;
		f = 1 ;
		//cout << ll << " <-ll " ;
		//cout << ans << "return \n";
	}
	if ( n - l / 2 - 1 > 0 && f == 0 ){
		//cout << "> " << n - l/2 - 1 << " " << l/2 << endl ;
		 cow ( n - l/2 - 1 , l / 2 ) ;
	}
	if ( n - l/2 - 1 == 0 && !f ) {
		//cout << "== " << n/2 << " " << n /2 <<endl ;
		cow ( l / 2 , l/2) ;
	}
}