AT_past202212_i 背の順

There are $ N $ people numbered $ 1 $ to $ N $ . You are given $ N $ pieces of information, each in this form: person $ A_i $ is taller than person $ B_i $ . Determine whether they are consistent.

The input is given from Standard Input in the following format: > $ N $ $ M $ $ A_1 $ $ B_1 $ $ \vdots $ $ A_M $ $ B_M $

If the given pieces of information are consistent, print `Yes`; otherwise, print `No`.

### Sample Explanation 1 It does not hold simultaneously that person $ 1 $ is taller than person $ 2 $ , person $ 2 $ is taller than person $ 3 $ , and person $ 3 $ is taller than person $ 1 $ . ### Sample Explanation 2 The same piece of information may be given multiple times. ### Constraints - $ 2 \leq N \leq 100 $ - $ 0 \leq M \leq 100 $ - $ 1 \leq A_i,B_i \leq N $ - $ A_i \neq B_i $ - All values in the input are integers.