题解

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,num,i;
string str;
int main(){
    cin>>str >> n;
    num = str.length();
    while(num < n){
        i=num;
        while(n>i) i*=2;
        i/=2;
        n-=(i+1);
        if(n==0) n=i;
    }
    cout<<str[n-1]<<endl;
    return 0;
}