Problem:
Score : 200 points

Problem Statement

You have an integer variable x.
Initially, x=0.

Some person gave you a string S of length N, and using the string you performed the following operation N times.
In the i-th operation, you incremented the value of x by 1 if S_i=I, and decremented the value of x by 1 if S_i=D.

Find the maximum value taken by x during the operations (including before the first operation, and after the last operation).

Constraints

1≤N≤100

|S|=N

No characters except I and D occur in S.

Input

The input is given from Standard Input in the following format:

N
S

Output

Print the maximum value taken by x during the operations.

Sample Input 1

5
IIDID

Sample Output 1

2

After each operation, the value of x becomes 1, 2, 1, 2 and 1, respectively. Thus, the output should be 2, the maximum value.

Sample Input 2

7
DDIDDII

Sample Output 2

0

The initial value x=0 is the maximum value taken by x, thus the output should be 0.

Solution in Ruby (2.3.3) (judge verdict: Accepted)

require 'pp'

def gets; ARGF.gets; end

class Solver

  def main
    n = gets.chomp.to_i
    s = gets.chomp

    ans = 0
    x = 0
    s.each_char do |c|
      if c == 'I'
        x += 1
        ans = x if ans < x
      else
        x -= 1
      end
    end

    puts ans
  end
end

if __FILE__ == $0
  Solver.new.main
end