## MRECAMAN - Recaman’s Sequence

English | Vietnamese |

The Recaman’s sequence is deﬁned by a0 = 0 ; for m > 0, a(m) = a(m−1) − m if the resulting a(m) is positive and not already in the sequence, otherwise a(m) = a(m−1) + m. The ﬁrst few numbers in the Recaman’s Sequence is 0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9 · · · .

Given k, your task is to calculate a(k).

### Input

The input consists of several test cases. Each line of the input contains an integer k where 0 ≤ k ≤ 500000. The last line contains an integer −1, which should not be processed.

Sample Input7 10000 -1

### Output

For each k given in the input, print one line containing a(k) to the output.

Sample output20 18658

Added by: | psetter |

Date: | 2009-02-23 |

Time limit: | 1s |

Source limit: | 50000B |

Memory limit: | 1536MB |

Cluster: | Cube (Intel G860) |

Languages: | All except: ERL JS-RHINO NODEJS PERL6 VB.NET |

Resource: | Pre Shanghai 2004 |