#include <iostream>
#include <algorithm>
#include <stack>

int main(){
	std::stack<int> balls;
	int n, current_ball, extracted_ball;
	bool stop;

	std::cin >> n;

	current_ball = 1;
	while(n){
		std::cin >> extracted_ball;
		if(balls.empty()){
			balls.push(current_ball);
			current_ball++;
		}
		while(current_ball < n && balls.top() != extracted_ball){
			balls.push(current_ball);
			current_ball++;
		}
		if(balls.top() == extracted_ball) balls.pop();
		n--;	//Условие остановки - просмотрели всю последовательность
	}
	if(balls.empty())
		std::cout << "Not a proof" << std::endl;
	else
		std::cout << "Cheater" << std::endl;

	int pause;
	std::cin >> pause;
}