// Problem   Genetic Code// Algorithm Backtracking// Runtime   O(3^n)// Author    Walter Guttmann// Date      12.03.2003#include <cassert>#include <cstring>#include <fstream>#include <iostream>using namespace std;ifstream in("genetic.in");char s[8192], *end=s, *target=s+5000;bool isThue(){  for (int len=1 ; end-len-len>=s ; len++)    if (strncmp(end-len-len, end-len, len) == 0)      return false;  return true;}bool backtrack(){  if (end == target)    return true;  ++end;  for (end[-1]='N' ; end[-1]<='P' ; end[-1]++)    if (isThue() && backtrack())      return true;  --end;  return false;}int main(){  backtrack();  int n;  while (in >> n)  {    if (n == 0) break;    assert(1 <= n && n <= 5000);    cout.form("%.*s\n", n, s);  }  return 0;}