又到3月14日，Happy π Day ! 每年MIT（麻省理工）总选择在这一天的1点59分放榜，又是几家欢乐几家愁。
π是一个神奇的数字，有很多人用能被背到小数点后多少位数来炫耀记忆力......
Pi (π) is the ratio of a circle’s circumference to its diameter. Pi is a constant number, meaning that for all circles of any size, Pi will be the same.
The diameter of a circle is the distance from edge to edge, measuring straight through the center. The circumference of a circle is the distance around.
2014年，π已经被算到了小数点后13,300,000,000,000位。
