## MONSTER - Monster Trap

Once upon a time when people still believed in magic, there was a great wizard Aranyaka Gondlir.
After twenty years of hard training in a deep forest, he had finally mastered ultimate magic, and
decided to leave the forest for his home.

Arriving at his home village, Aranyaka was very surprised at the extraordinary desolation. A gloom
had settled over the village. Even the whisper of the wind could scare villagers. It was a mere
shadow of what it had been.

What had happened? Soon he recognized a sure sign of an evil monster that is immortal. Even
the great wizard could not kill it, and so he resolved to seal it with magic. Aranyaka could cast a
spell to create a monster trap: once he had drawn a line on the ground with his magic rod, the line
would function as a barrier wall that any monster could not get over. Since he could only draw
straight lines, he had to draw several lines to complete a monster trap, i.e., magic barrier walls
enclosing the monster. If there was a gap between barrier walls, the monster could easily run away
through the gap.

For instance, a complete monster trap without any gaps is built by the barrier walls in the left
figure, where “M” indicates the position of the monster. In contrast, the barrier walls in the right
figure have a loophole, even though it is almost complete.

Your mission is to write a program to tell whether or not the wizard has successfully sealed the
monster.

### Input

The input consists of multiple data sets, each in the following format.

The first line of a data set contains a positive integer n, which is the number of the line segments
drawn by the wizard. Each of the following n input lines contains four integers x, y, x , and
y , which represent the x– and y–coordinates of two points (x, y) and (x , y ) connected by a line
segment. You may assume that all line segments have non–zero lengths. You may also assume that
n is less than or equal to 100 and that all coordinates are between −50 and 50, inclusive.

For your convenience, the coordinate system is arranged so that the monster is always on the origin
(0, 0). The wizard never draws lines crossing (0, 0).

You may assume that any two line segments have at most one intersection point and that no three
line segments share the same intersection point. You may also assume that the distance between
any two intersection points is greater than 10^−5 .

An input line containing a zero indicates the end of the input.

### Output

For each data set, print “yes” or “no” in a line. If a monster trap is completed, print “yes”. Otherwise, i.e., if there is a loophole, print “no”.

### Example

Input:8 -7 9 6 9 -5 5 6 5 -10 -5 10 -5 -6 9 -9 -6 6 9 9 -6 -1 -2 -3 10 1 -2 3 10 -2 -3 2 -3 8 -7 9 5 7 -5 5 6 5 -10 -5 10 -5 -6 9 -9 -6 6 9 9 -6 -1 -2 -3 10 1 -2 3 10 -2 -3 2 -3 0Output:yes no

Added by: | Daniel Gómez Didier |

Date: | 2008-11-18 |

Time limit: | 1s |

Source limit: | 50000B |

Memory limit: | 1536MB |

Cluster: | Cube (Intel G860) |

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

Resource: | 2008 PUJ - Circuito de Maratones ACIS / REDIS |