N recruits are standing in front of a sergeant who orders to turn left. Some of the soldiers turn left, while the others turn right. In a second each recruit seeing the face of another recruit understands that a mistake was made and turns around. This happens at the same time to each pair of soldiers facing each other. The process continues until the formation becomes stable. Write a program, which finds out the number of times when a pair of soldiers turned around. If the process is infinite then the program should write the word “NO”.
Example:
Legend:
‘<’: a recruit facing left;
‘>’: a recruit facing right.
Formation |
Comments |
Number of turns |
> > < < > < |
Initial formation |
2 |
> < > < < > |
One second has passed |
2 |
< > < > < > |
Two seconds have passed |
2 |
< < > < > > |
Three seconds have passed |
1 |
< < < > > > |
Final formation |
Total: 7 |
Input
The first line contains the number of recruits (N). The rest of the input contains only ‘<’, ‘>’ and line break characters. There is exactly N ‘<’ and ‘>’ characters in the input. Each line of the input may have up to 255 characters.
1 ≤ N ≤ 30000.
Output
Write the number of turns.
Sample
Problem Source: Quarterfinal, Central region of Russia, Rybinsk, October 17-18 2001