//#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <algorithm>
#include <fstream>
#include <string>
#include <vector>
#include <iomanip>

using namespace std;

int a[100500];
int v[100500];

int main() {
	ios::sync_with_stdio(0);
	int n;
	cin >> n;
	for (int i = 0; i < n; ++i) {
	   cin >> a[i];
	}
	int i = 0, iter = -1;
	for (int cur = 1; cur <= n; ++cur) {
	   if (i >= n)
	      break;
	   if (iter < 0)
	      iter = -1;
	   iter++;
	   v[iter] = cur;
	   while(a[i] == v[iter]) {
	      if (i >= n || iter < 0)
	         break;
         i++;
         iter--;
	   }
	}

	if (iter < 0) {
      cout << "Not a proof";
	   return 0;
	}
	cout << "Cheater";
	return 0;
}