Dive Log Depth Recovery

A research submersible starts every mission at the surface, depth 0, and its onboard computer logs each maneuver in order as one of three kinds of command:

• the keyword asc — the submersible ascends one level; if it is already at the surface, this command has no effect and the depth stays 0;
• the keyword stay — the submersible holds its current depth;
• any other token, a chamber name made only of lowercase English letters — the submersible descends one level into a newly logged chamber.

After the whole mission log has been replayed in order, determine the minimum number of asc commands the submersible would still have to issue, one after another, to get back exactly to the surface (depth 0).

Input format

• Line 1: a single integer n, the number of commands in the log.
• Line 2: n space-separated tokens, each either asc, stay, or a chamber name of 1 to 10 lowercase English letters (guaranteed to differ from both keywords).

Output format

A single integer: the number of further asc commands required, i.e. the submersible's final depth after replaying the whole log.

Constraints

• 1 <= n <= 1000.
• Every chamber-name token has length between 1 and 10 and consists only of lowercase English letters.

5
alpha beta asc gamma stay

2

3
asc asc alpha

1