codeforces 569 D. Symmetric and Transitive (组合数学 第二类斯特林数 贝尔数)
D. Symmetric and Transitive
time limit per test
1.5 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Little Johnny has recently learned about set theory. Now he is studying binary relations. You’ve probably heard the term “equivalence relation”. These relations are very important in many areas of mathematics. For example, the equality of the two numbers is an equivalence relation.