package no.uib.ii.inf102.f18.mandatory1;

public class BSTDebugging {


	public static void main(String[] args) {
		Kattio io = new Kattio(System.in);
		int n = io.getInt();
		int key = io.getInt();
		int current = io.getInt();
		boolean valid = true;
		for(int i = 0; i < n - 1; i++) {
			int next = io.getInt();
			if(key >= current) {
				if(current >= next) {
					System.out.println("invalid");
					valid = false;
					break;
				}
			}
			else if (current == key) {
				break;
			}
			else {
				if(current <= next) {
					System.out.println("invalid");
					valid = false;
					break;
				}
			}
			current = next;
		}
		if(valid == true) {
			System.out.println("valid");
		}
	}
}