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 Julia (0.5.0) (judge verdict: Wrong Answer)

function main()
	n = parse(Int, readline())
	s = chomp(readline())
	a = Array{Int}(n)
    if s[1] == 'I'
    	a[1] = 1
    else
    	a[1] = -1
    end
	for i in 2:n
		if s[i] == 'I'
			a[i] = a[i-1] += 1
		else
			a[i] = a[i-1] -= 1
		end
	end
	println(max(maximum(a),0))
end

main()