#1 AC 其他 WA + TLE 代码求调

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) ;
    }
}