Language: C++

#include <iostream>
#include <string>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <vector>
#include <bitset>
#include <functional>
#include <queue>
#include <utility>

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define dump(x)  cerr << #x << " = " << (x) << endl;
typedef long long LL;

using namespace std;

int main(void)
{
	string S;

	cin >> S;

	/*
	int count = 0;
	bool flag = false;
	while(1){
		flag = false;
		for (int i = 0; i < S.size() - 1; i++) {
			if (S[i] != S[i + 1]) {
				S.erase(i, i + 1);
				i--;
				count += 2;
				flag = true;
				continue;
			}
		}
		if (flag == false) {
			break;
		}
	}

	cout << count << endl;
	*/

	unsigned int count = 0;
	FOR(i, 0, S.size()) {
		if (S[i] == '0') {
			count++;
		}
	}
	int ans = min(count, S.size() - count);

	cout << ans * 2 << endl;

	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:52:22: error: no matching function for call to 'min(unsigned int&, std::__cxx11::basic_string<char>::size_type)'
   52 |         int ans = min(count, S.size() - count);
      |                   ~~~^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 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:52:22: note:   deduced conflicting types for parameter 'const _Tp' ('unsigned int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'})
   52 |         int ans = min(count, S.size() - count);
      |                   ~~~^~~~~~~~~~~~~~~~~~~~~~~~~
/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,
                 from a.cc:3:
/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:52:22: note:   mismatched types 'std::initializer_list<_Tp>' and 'unsigned int'
   52 |         int ans = min(count, S.size() - count);
      |                   ~~~^~~~~~~~~~~~~~~~~~~~~~~~~