```
Topic id is a sequence <number>.<number>. ... <number>. All numbers are integers from a segment [1, 20] and have no leading zeroes. All topic id’s are unique.
```
try test:
1. graphs
1022
1065
2. geometry
1020
2.1. idea
1130
2.2. technique
1111 1065
1265
2.2.1. convex hull
1271
3. dynamic programming
1244
20. vector