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)

include Math
define_method :max, 		-> (a,b) { a > b ? a : b }
define_method :min, 		-> (a,b) { a < b ?  a : b }
define_method :swap, 		-> (a,b) { a, b = b, a }
define_method :gi, 			-> () { gets.split.map(&:to_i) }
define_method :gs, 			-> () { gets.chomp }
define_method :getc,		-> () { gets.chomp.split('') }
define_method :fi, 			-> () {first}
define_method :darray,	-> (size1, size2, init = nil) { Array.new(size1){Array.new(size2){init}} }
define_method :array,		-> (size,init = nil) { Array.new(size){init} }
define_method :putall, 	-> (obj) { obj.each { |o| puts o } }
define_method :repl, 		-> (st,en, &block) { st.upto en-1 do |i| block.call(i) end }
define_method :rep, 		-> (num, &block) { num.times do |i| block.call(i) end }

	n = gi[0]
	str = getc
	ans = 0
	data = 0
	str.each do |obj|
		case obj
		when 'D'
			data -= 1
		when 'I'
			data += 1
		end
		ans = data if ans < data
	end

	puts ans