#include <bits/stdc++.h>
using namespace std;
int main()
{ string s;
int c=0,myvariable;
level:

cout<<"enter any string: ";
cin>>s;
if( (s[0]>='a'&&s[0]<='z')||(s[0]>='A'&&s[0]<='Z')||(s[0]=='_') )
 {
   for(int i=1;i<s.length();i++)
   {

     if((s[i]>='a'&& s[i]<='z')||(s[i]>='A' && s[i]<='Z')||(s[i]>='0'&& s[i]<='9')||(s[i]=='_') )
{
 c++;
}}
if(c==s.length()){
myvariable=0;
}}else
{myvariable=1;
}
if(myvariable==1)
cout<<s<<"is not valid identifier"<<endl;
else
cout<<s<<" is valid identifier"<<endl;
goto level;
return 0;
}