#include<iostream>
#include<iomanip>
#include<string>
using namespace std;
class Check
{
    public:
     string str = "";
     string st = "";
    public:
     Check()
     {
         for(int i=0;i<str.length();i++)
         {
         if(str.empty())
         {
             cout<<"Invalid input";
             
         }
         if((str >= 'a' && str <= 'z') ||(str >= 'A' && str <= 'Z')
         {
             continue;
         }
         if(!(str[i]== '0'||str[i]== '1'||str[i]== '2'||str[i]== '3'||str[i]== '4'||str[i]== '5'||str[i]== '6'||
         str[i]== '7'||str[i]== '8'||str[i]== '9'))
         {
             st += str[i];
         }
         else
         {
             cout<<"Invalid input";
             
         }
         }
         cout<<st;
     }
};
int main()
{
    Check c1;
    return 0;
}