#include<bits/stdc++.h>
using namespace std;
int main()
{
 
    char a[1000];
    bool f=0;
 
   while( gets(a))
    {
 
    f=0;
    if(a[0]>='0'&&a[0]<='9')
        f=1;
    else
    {
    for(int i=1;a[i]!='\0';i++)
    {
 
        if((a[i]>='a'&&a[i]<='z')||(a[i]>='A'&&a[i]<='Z')
           ||(a[i]>='0'&&a[i]<='9')||a[i]=='_')
        {
                f=0;
        }
        else
           {
 
            f=1;
            break;
           }
 
}
    }
    if(f==1)
        cout<<"This is not an identifier\n";
    else
        cout<<"This is an identifier\n";
    }
}