Pile

#include <iostream>
#include <vector>
using namespace std;
int n;

vector<int> pile;

bool tp(int a){
  if (pile.size()==0) return 0;
  else return pile[pile.size()-1]==a;
}


int main(){
  cin >> n;
  bool cheated=0;
  int l=1;
  for (int i=0; i<n; ++i){
    int a;
    cin >> a;
    if (tp(a)){
      pile.pop_back();
    }else{
      if (a<l){
	cheated=1;
	continue;
      }
      for (int k=l; k<a; ++k){
	pile.push_back(k);
      }
      l=a+1;
    }
  }
  if (!cheated) cout << "Not a proof\n";
  else cout << "Cheater\n";
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED