#include<iostream>
#include<cctype>
using namespace std;
int main()
{
    string name;
    getline(cin,name);
    for(int i=0;i<=name.length();i++)
    {
    if(!isalpha(name))
    {
        cout<<"Invalid input";
    }
    else
    {
        cout<<"OK";
    }
    }
}