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)

N = gets.to_i
S = gets.chomp
A = S.split("")
a = Array.new
for i in 0..N-1
    if i == 0 
        if A[i] == 'I'
            a[i] = 1
        elsif A[i] == 'D'
            a[i] = -1
        end
    else
        if A[i] == 'I'
            a[i] = a[i-1] + 1
        else A[i] == 'D'
            a[i] = a[i-1] - 1
        end
    end
end
if a.max > 0
    puts a.max
else 
    puts 0
end