Language: C++

#include "bits/stdc++.h"
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
#define int ll
#define double long double
#define YES {cout<<"YES"<<'\n';}
#define NO {cout<<"NO"<<'\n';}
#define Yes {cout<<"Yes"<<'\n';}
#define No {cout<<"No"<<'\n';}
#define yes {cout<<"yes"<<'\n';}
#define no {cout<<"no"<<'\n';}
void YN(bool flg){cout<<(flg?"YES":"NO")<<'\n';}
void Yn(bool flg){cout<<(flg?"Yes":"No")<<'\n';}
void yn(bool flg){cout<<(flg?"yes":"no")<<'\n';}
#define SORT(a) sort(a.begin(),a.end())
#define REVERSE(a) reverse(a.begin(),a.end())
#define REP(i, n) for(int i = 0; i < n; i++)
#define REPR(i, n) for(int i = n; i >= 0; i--)
#define FOR(i, m, n) for(int i = m; i < n; i++)
#define out(n) {cout << n << '\n';}
typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<bool> VB;
typedef vector<VI> VVI;
const int MOD = 1000000007;
const long long INF = 10e10;
const double PI = acos(-1.0);
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T>auto MAX(const T& a) { return *max_element(a.begin(),a.end()); }
template<class T>auto MIN(const T& a) { return *min_element(a.begin(),a.end()); }
int ABS(int a) {if(a<0) a = -a; return a;}
template<class T, class U>U SUM(const T& a, const U& v) { return accumulate(a.begin(),a.end(), v); }
template<class T, class U>U COUNT(const T& a, const U& v) { return count(a.begin(),a.end(), v); }
template<class T, class U>int LOWER(const T& a, const U& v) { return lower_bound(a.begin(),a.end(), v) - a.begin(); }
template<class T, class U>int UPPER(const T& a, const U& v) { return upper_bound(a.begin(),a.end(), v) - a.begin(); }
int GCD(int a, int b) { return b ? GCD(b, a%b) : a; }
int LCM(int a, int b) { int g = GCD(a, b); return a / g * b; }
int POW(int a, int n) { int r = 1; while (n > 0) { if (n & 1)r *= a; a *= a; n /= 2; }return r; }
int isPrime(int n){if(n<2){return 0;}for(int i=2; i*i<=n; i++){if(n%i==0){return 0;}}return 1;}
/*素因数分解*/map< int, int >prime_factor(int n){map< int, int > ret;for(int i = 2; i * i <= n; i++) {while(n % i == 0) {ret[i]++;n /= i;}}if(n != 1) ret[n] = 1;return ret;}
/*約数の個数*/int divisor_number(int n){auto p = prime_factor(n); int res = 1; for(auto x:p)res*=(x.second+1); return res;}
/*約数列挙*/vector<int> divisor(int n){vector<int> v; for(int i=1; i*i<=n; i++){if(n%i==0){v.push_back(i);if(i!=n/i){v.push_back(n/i);}}}sort(v.begin(),v.end()); return v;}
//----------------ライブラリとか----------------

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout<<fixed<<setprecision(15);

    string s; int k; cin >> s >> k;
    REP(i,min(s.size(),k)) if(s[i]>='2'){out(s[i]); return 0;}
    out(1);

    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:53:14: error: no matching function for call to 'min(std::__cxx11::basic_string<char>::size_type, ll&)'
   53 |     REP(i,min(s.size(),k)) if(s[i]>='2'){out(s[i]); return 0;}
      |           ~~~^~~~~~~~~~~~
a.cc:18:38: note: in definition of macro 'REP'
   18 | #define REP(i, n) for(int i = 0; i < n; i++)
      |                                      ^
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:233:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)'
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
a.cc:53:14: note:   deduced conflicting types for parameter 'const _Tp' ('long unsigned int' and 'll' {aka 'long long int'})
   53 |     REP(i,min(s.size(),k)) if(s[i]>='2'){out(s[i]); return 0;}
      |           ~~~^~~~~~~~~~~~
a.cc:18:38: note: in definition of macro 'REP'
   18 | #define REP(i, n) for(int i = 0; i < n; i++)
      |                                      ^
/usr/include/c++/14/bits/stl_algobase.h:281:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)'
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5686:5: note: candidate: 'template<class _Tp> constexpr _Tp std::min(initializer_list<_Tp>)'
 5686 |     min(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5686:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5696:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::min(initializer_list<_Tp>, _Compare)'
 5696 |     min(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5696:5: note:   template argument deduction/substitution failed:
a.cc:53:14: note:   mismatched types 'std::initializer_list<_Tp>' and 'long unsigned int'
   53 |     REP(i,min(s.size(),k)) if(s[i]>='2'){out(s[i]); return 0;}
      |           ~~~^~~~~~~~~~~~
a.cc:18:38: note: in definition of macro 'REP'
   18 | #define REP(i, n) for(int i = 0; i < n; i++)
      |                                      ^