Problem:
Score : 200 points

Problem Statement

We have a string S of length N consisting of uppercase English letters.

How many times does ABC occur in S as contiguous subsequences (see Sample Inputs and Outputs)?

Constraints

3 \leq N \leq 50

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print number of occurrences of ABC in S as contiguous subsequences.

Sample Input 1

10
ZABCDBABCQ

Sample Output 1

2

Two contiguous subsequences of S are equal to ABC: the 2-nd through 4-th characters, and the 7-th through 9-th characters.

Sample Input 2

19
THREEONEFOURONEFIVE

Sample Output 2

0

No contiguous subsequences of S are equal to ABC.

Sample Input 3

33
ABCCABCBABCCABACBCBBABCBCBCBCABCB

Sample Output 3

5

Solution in C (Clang 3.8.0) (judge verdict: Accepted)

#include <stdio.h>

int main(void){

    int n, count=0;

    scanf("%d", &n);

    char s[n+3];

    scanf("%s", &s);

    for(int i=0;i<n+3;i++){
        if(s[i]=='A'){
            i++;
            if(s[i]=='B'){
                i++;
                if(s[i]=='C'){
                    count++;
                }else{
                    i--;
                }
            }else{
                i--;
            }
        }
    }

    printf("%d", count);
}