ural 1494 Monobilliards

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

int a[200000],b[200000];
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        for(int i=1; i<=n; i++)
            scanf("%d",a+i);
        int top=0,top1=1;
        for(int i=1; i<=n; i++)
        {
            b[++top]=i;
            while(top&&b[top]==a[top1]){
               top--;top1++;
            }
        }
        if(top) printf("Cheater
");
        else printf("Not a proof
");
    }
    return 0;
}