#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;

int main()
{
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
	int n;
	vector<int> now;
	now.push_back(1);
	int last = 1;
	cin >> n;
	for(int i = 0; i < n; i++)
	{
		int buf;
		cin >> buf;
		if(!now.empty() && (now.back() > buf))
		{
			cout << "Cheater";
			return 0;
		}
		while(now.empty() || (now.back() != buf))
		{
			now.push_back(last + 1);
			last++;
		}
		if(now.back() == buf)
			now.pop_back();
	}
	cout << "Not a proof";
}