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)

def solve(x,m,n,str)
	str.split("").each do |c|
		if c=="D"
			x-=1
		elsif c=="I"
			x+=1
			if x>m then m=x end
		end
	end
	p m
end


if __FILE__==$0
	read_i=lambda{|s|s.strip.to_i}
	read_s=lambda{|s|s.strip}
	n=read_i[gets]
	str=read_s[gets]
	solve(0,0,n,str)
end