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 Rust (1.15.1) (judge verdict: Wrong Answer)

use std::io::Read;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();

    let mut iter = buf.split_whitespace();

    let _n: usize = iter.next().unwrap().parse().unwrap();
    let s: String = iter.next().unwrap().parse().unwrap();

    let mut count: usize = 0;
    let mut abc_count: usize = 0;
    for x in s.chars() {
        match x {
            'A' => {
                if abc_count == 0 {
                    abc_count = 1;
                }
            },
            'B' => {
                if abc_count == 1 {
                    abc_count = 2;
                }
            },
            'C' => {
                if abc_count == 2 {
                    abc_count = 0;
                    count += 1;
                }
            },
            _ => {}
        }
    }

    println!("{}", count);
}