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 Ruby (2.3.3) (judge verdict: Accepted)

# Wrote in Mar 5, 2020 21:48 by reetok
require 'time'
require 'prime'
require 'bigdecimal'
def inp(type=:to_i,spst=" ")
  return eval("gets.chomp.split(#{spst}).map(&:#{type})")
end
def inpf() return self.inp(:to_f," ") end
def inps() return self.inp(:to_s," ") end
def r_up(a, b) (a/b).ceil end
def r_down(a, b) (a/b).floor end
def sum(a) a.inject(:+) end
def big(a,b) return (a>b)? a:b end
def small(a,b) return (a<b)? a:b end
def minp(n,datatype=".to_i")
  t = []
  n.times do
    t.push(eval("gets.chomp#{datatype}"))
  end
  return t
end
def yes() puts "Yes" end
def no() puts "No" end
def ynju(bool,yes="Yes",no="No") puts (bool ? yes : no) end
class Integer
  def divisor_list
    devisors = [1]
    2.upto(self/2) do |i|
      devisors << i if self%i == 0
    end
    devisors << self
    return devisors.uniq.sort
  end
end
class Array
  def upper(a) #aより上
    self.sort.select{|n|n>=a}
  end
  def downer(a) #aより下
    self.sort.select{|n|n<=a}
  end
end

#---------------

n = gets.to_i
s = gets.to_s

puts s.scan('ABC').length