def main():
S = input()
vals = {'A': 1, 'B': 2, 'C': 3}
st = SortedSet([(vals[c], i) for i, c in enumerate(S)])
ans = 0
while len(st):
v, i = st.pop(0)
if v == 1:
if st.ge((v + 1, i)) is not None:
w, j = st.ge((v + 1, i))
if st.ge((w + 1, j)) is not None:
x, k = st.ge((w + 1, j))
ans += 1
st.discard((w, j))
st.discard((x, k))
print(ans)
# https://github.com/tatyam-prime/SortedSet/blob/main/codon/SortedSet.py
import math
from bisect import bisect_left, bisect_right
from typing import ClassVar, Generator, Optional
class SortedSet[T]:
size: int
a: list[list[T]]
BUCKET_RATIO: ClassVar[int] = 16
SPLIT_RATIO: ClassVar[int] = 24
def __init__(self) -> None:
self.size = 0
self.a = []
def __init__(self, a: Generator[T]) -> None:
self.__init__(list(a))
def __init__(self, a: list[T]) -> None:
"Make a new SortedSet from a list. / O(N) if sorted and unique / O(N log N)"
n = len(a)
if any(a[i] > a[i + 1] for i in range(n - 1)):
a.sort()
if any(a[i] >= a[i + 1] for i in range(n - 1)):
a, b = [], a
for x in b:
if not a or a[-1] != x:
a.append(x)
n = self.size = len(a)
num_bucket = int(math.ceil(math.sqrt(n / self.BUCKET_RATIO)))
self.a = [a[n * i // num_bucket : n * (i + 1) // num_bucket] for i in range(num_bucket)]
def __iter__(self) -> Generator[T]:
for i in self.a:
for j in i: yield j
def __reversed__(self) -> Generator[T]:
for i in reversed(self.a):
for j in reversed(i): yield j
def __eq__(self, other: SortedSet[T]) -> bool:
if len(self) != len(other): return False
for x, y in zip(self, other):
if x != y: return False
return True
def __ne__(self, other: SortedSet[T]) -> bool:
return not self.__eq__(other)
def __len__(self) -> int:
return self.size
def __repr__(self) -> str:
return "SortedSet" + str(self.a)
def __str__(self) -> str:
s = str(list(self))
return "{" + s[1 : len(s) - 1] + "}"
def _position(self, x: T) -> tuple[list[T], int, int]:
"return the bucket, index of the bucket and position in which x should be. self must not be empty."
for i, a in enumerate(self.a):
if x <= a[-1]: break
return (a, i, bisect_left(a, x))
def __contains__(self, x: T) -> bool:
if self.size == 0: return False
a, _, i = self._position(x)
return i != len(a) and a[i] == x
def add(self, x: T) -> bool:
"Add an element and return True if added. / O(√N)"
if self.size == 0:
self.a = [[x]]
self.size = 1
return True
a, b, i = self._position(x)
if i != len(a) and a[i] == x: return False
a.insert(i, x)
self.size += 1
if len(a) > len(self.a) * self.SPLIT_RATIO:
mid = len(a) >> 1
self.a[b:b+1] = [a[:mid], a[mid:]]
return True
def _pop(self, a: list[T], b: int, i: int) -> T:
ans = a.pop(i)
self.size -= 1
if not a: del self.a[b]
return ans
def discard(self, x: T) -> bool:
"Remove an element and return True if removed. / O(√N)"
if self.size == 0: return False
a, b, i = self._position(x)
if i == len(a) or a[i] != x: return False
self._pop(a, b, i)
return True
def lt(self, x: T) -> Optional[T]:
"Find the largest element < x, or None if it doesn't exist."
for a in reversed(self.a):
if a[0] < x:
return a[bisect_left(a, x) - 1]
def le(self, x: T) -> Optional[T]:
"Find the largest element <= x, or None if it doesn't exist."
for a in reversed(self.a):
if a[0] <= x:
return a[bisect_right(a, x) - 1]
def gt(self, x: T) -> Optional[T]:
"Find the smallest element > x, or None if it doesn't exist."
for a in self.a:
if a[-1] > x:
return a[bisect_right(a, x)]
def ge(self, x: T) -> Optional[T]:
"Find the smallest element >= x, or None if it doesn't exist."
for a in self.a:
if a[-1] >= x:
return a[bisect_left(a, x)]
def __getitem__(self, i: int) -> T:
"Return the i-th element."
if i < 0:
for a in reversed(self.a):
i += len(a)
if i >= 0: return a[i]
else:
for a in self.a:
if i < len(a): return a[i]
i -= len(a)
raise IndexError("index out of range")
def pop(self, i: int = -1) -> T:
"Pop and return the i-th element."
if i < 0:
for b, a in enumerate(reversed(self.a)):
i += len(a)
if i >= 0: return self._pop(a, ~b, i)
else:
for b, a in enumerate(self.a):
if i < len(a): return self._pop(a, b, i)
i -= len(a)
raise IndexError("index out of range")
def index(self, x: T) -> int:
"Count the number of elements < x."
ans = 0
for a in self.a:
if a[-1] >= x:
return ans + bisect_left(a, x)
ans += len(a)
return ans
def index_right(self, x: T) -> int:
"Count the number of elements <= x."
ans = 0
for a in self.a:
if a[-1] > x:
return ans + bisect_right(a, x)
ans += len(a)
return ans
if __name__ == "__main__":
main()