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: Accepted)

// Template from https://techracho.bpsinc.jp/jhonda/2019_08_05/78537

// input macro for competive-programming from https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[allow(unused_macros)]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        input_inner!{$s, $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };

    ($iter:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, bytes) => {
        read_value!($iter, String).into_bytes()
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

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

    println!("{}", solve(&s));
}

macro_rules! test {
    ($($exp_input:expr => $output:expr),* $(,)*) => {
        #[test]
        fn solve_test() {
            $(
                let start = std::time::Instant::now();
                let input = solve($exp_input);
                let end = start.elapsed();
                assert_eq!(input, $output, "{}.{:03}", end.as_secs(), end.subsec_millis());
                assert!(end.as_secs() <= 2, "expected_sec: {}sec, actual_sec: {}sec", 2, end.as_secs());
                assert!(end.as_secs() <= 1, "expected_sec: {}sec, actual_sec: {}sec", 1, end.as_secs());
                assert!(end.subsec_millis() <= 10, "expected_ms: {}ms, actual_ms: {}ms", 10, end.subsec_millis());
                assert!(end.subsec_millis() <= 2, "expected_ms: {}ms, actual_ms: {}ms", 2, end.subsec_millis());
            )*
        }
    };
}

test! {
r#"10
ZABCDBABCQ"# => r#"2"#,

r#"19
THREEONEFOURONEFIVE"# => r#"0"#,

r#"33
ABCCABCBABCCABACBCBBABCBCBCBCABCB"# => r#"5"#,
}

fn solve(src: &str) -> String {
    let mut src_iter = src.split_whitespace();
    input! {
        source = src_iter,
        _n: usize,
        s: String,
    }

    s.matches("ABC").count().to_string()
}