#include <bits/stdc++.h>
using namespace std;
bool isValid(string str, int n)
{

	if (!((str[0] >= 'a' && str[0] <= 'z')
		|| (str[0] >= 'A' && str[0] <= 'Z')
		|| str[0] == '_'))
		return false;

	
	for (int i = 1; i < str.length(); i++) {
		if (!((str[i] >= 'a' && str[i] <= 'z')
			|| (str[i] >= 'A' && str[i] <= 'Z')
			|| (str[i] >= '0' && str[i] <= '9')
			|| str[i] == '_'))
			return false;
	}


	return true;
}

int main()
{
	string str = "geeks123";
	int n = str.length();

	if (isValid(str, n))
		cout << "Valid";
	else
		cout << "Invalid";

	return 0;
}