Unknown Error了，但在AtCoder上测AC，求助

# include<bits/stdc++.h>
using namespace std;
string s;
int main()
{
	int len,s1=0,s2=0;
	cin>>s;
	len=s.size();
	for(int i=0;i<=len-1;i++)
	{
		if(s[i]=='0')
		{
			s1++;
		}
		else
		{
			s2++;
		}
	}
	if(s1<s2)
	{
		cout<<s1*2;
	}
	else
	{
		cout<<s2*2;
	}
	return 0;
}