kthnum.cpp

//#include<bits/stdc++.h>
#include<iostream>
#include<string>
#include<algorithm>

#define long long long
#define nln '\n'

using namespace std;

string num2string(long num)
{
    string str = "";
    while (num > 0)
    {
        str += (num%10)+'0';
        num /= 10;
    }
    reverse(str.begin(), str.end());
    return str;
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);
    cout.tie(0)->sync_with_stdio(0);

    long n, k, len = 0;
    cin >> n >> k;
    string st1 = "", st2 = "";
    for (long i = 1; i <= n; ++i)
    {
        st2 = num2string(i) + st1 + st1;
        len += abs((long)st1.size()-(long)st2.size());
        st1 = st2;
        if ((long)st1.size() > k)
            st1.erase(st1.begin()+k+1, st1.end());
    }

    if (k > len)
        cout << "-1" << nln;
    else
        cout << st2[k-1] << nln;

    return 0;
}