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 C (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <stdio.h>

int main(void){

  long long N,i;
  long long x = 0;
  long long max = 0;
  scanf("%lld",&N);
  char S[N];
  
  for(i=0;i<N;i++){
  	scanf("%c",&S[i]);
  }
  
  for(i=0;i<=N;i++){
    if(S[i]=='D'){
      --x;
    }
    else if(S[i]=='I') ++x;
    if(x>max){
      max = x;
    }
  }
  printf("%lld",max);
  
  return 0;
  
}