e-olymp
Competitions

ADA Training - October 7

Arrangement of Contest

Little Dmitry and little Petr want to arrange a contest. Their little friends submitted several task proposals and now Dmitry and Petr want to select some of them for the contest. As they are just little boys, they cannot estimate quality of tasks, but they know for sure that in good contest title of the first problem starts with A, the title of the second one - with B, and so on.

Given titles of the proposed tasks, help little brothers to determine the maximal number of problems in a *good *contest they can arrange.

Input

The first line contains single integer n - the number of problem proposals received by the little brothers (1n100).

Next n lines contain titles of proposed problems, one per line. The length of each title does not exceed 30 characters. Each title starts with an uppercase letter and contains only English letters, digits and underscores.

Output

Output a single number - the maximal number of problems in a good contest. In case there is no good contest that may be arranged, output 0.

Time limit 1 second
Memory limit 64 MiB
Input example #1
12
Arrangement_of_Contest
Ballot_Analyzing_Device
Correcting_Curiosity
Dwarf_Tower
Energy_Tycoon
Flight_Boarding_Optimization
Garage
Heavy_Chain_Clusterization
Intellectual_Property
J
Kids_in_a_Friendly_Class
Lonely_Mountain
Output example #1
12
Input example #2
3
Snow_White_and_the_7_Dwarfs
A_Problem
Another_Problem
Output example #2
1
Input example #3
2
Good_Problem
Better_Problem
Output example #3
0
Source 2013 ACM NEERC, Northern Subregional Contest, St Petersburg, October 26, Problem A