String to leading 0

string qu0(string a)
{ ll n; 
 if(a.size()>=2&&a[0]=='0')
  {  n=a.size();
	for(int i=0;i<n;i++)
	 { if(a[i]!='0')break;
	 	else{a.erase(a.begin());i--;}
	 }
	
  }
	return a;		
}