output_description: Print the maximum value taken by x during the operations.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      N
      S
attempt: n = int(input())
  s = input()
  ans = 0
  cur = 0
  for c in s:
  	if c == 'I':
  		cur += 1
          ans = max(ans, cur)
      else:
  		cur -= 1
            
  print(ans)
problem_description: 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).
samples: [{"input": "5\n    IIDID", "output": "2\n    \n\nAfter each operation, the value of x becomes 1, 2, 1, 2 and 1, respectively.\nThus, the output should be 2, the maximum value.\n\n* * *"}, {"input": "7\n    DDIDDII", "output": "0\n    \n\nThe initial value x=0 is the maximum value taken by x, thus the output should\nbe 0."}]