import sys
input = sys.stdin.readline

from collections import defaultdict

import typing

def _ceil_pow2(n: int) -> int:
    x = 0
    while (1 << x) < n:
        x += 1

    return x


def _bsf(n: int) -> int:
    x = 0
    while n % 2 == 0:
        x += 1
        n //= 2

    return x


class SegTree:
    def __init__(self,
                 op: typing.Callable[[typing.Any, typing.Any], typing.Any],
                 e: typing.Any,
                 v: typing.Union[int, typing.List[typing.Any]]) -> None:
        self._op = op
        self._e = e

        if isinstance(v, int):
            v = [e] * v

        self._n = len(v)
        self._log = _ceil_pow2(self._n)
        self._size = 1 << self._log
        self._d = [e] * (2 * self._size)

        for i in range(self._n):
            self._d[self._size + i] = v[i]
        for i in range(self._size - 1, 0, -1):
            self._update(i)

    def set(self, p: int, x: typing.Any) -> None:
        assert 0 <= p < self._n

        p += self._size
        self._d[p] = x
        for i in range(1, self._log + 1):
            self._update(p >> i)

    def get(self, p: int) -> typing.Any:
        assert 0 <= p < self._n

        return self._d[p + self._size]

    def prod(self, left: int, right: int) -> typing.Any:
        assert 0 <= left <= right <= self._n
        sml = self._e
        smr = self._e
        left += self._size
        right += self._size

        while left < right:
            if left & 1:
                sml = self._op(sml, self._d[left])
                left += 1
            if right & 1:
                right -= 1
                smr = self._op(self._d[right], smr)
            left >>= 1
            right >>= 1

        return self._op(sml, smr)

    def all_prod(self) -> typing.Any:
        return self._d[1]

    def max_right(self, left: int,
                  f: typing.Callable[[typing.Any], bool]) -> int:
        assert 0 <= left <= self._n
        assert f(self._e)

        if left == self._n:
            return self._n

        left += self._size
        sm = self._e

        first = True
        while first or (left & -left) != left:
            first = False
            while left % 2 == 0:
                left >>= 1
            if not f(self._op(sm, self._d[left])):
                while left < self._size:
                    left *= 2
                    if f(self._op(sm, self._d[left])):
                        sm = self._op(sm, self._d[left])
                        left += 1
                return left - self._size
            sm = self._op(sm, self._d[left])
            left += 1

        return self._n

    def min_left(self, right: int,
                 f: typing.Callable[[typing.Any], bool]) -> int:
        assert 0 <= right <= self._n
        assert f(self._e)

        if right == 0:
            return 0

        right += self._size
        sm = self._e

        first = True
        while first or (right & -right) != right:
            first = False
            right -= 1
            while right > 1 and right % 2:
                right >>= 1
            if not f(self._op(self._d[right], sm)):
                while right < self._size:
                    right = 2 * right + 1
                    if f(self._op(self._d[right], sm)):
                        sm = self._op(self._d[right], sm)
                        right -= 1
                return right + 1 - self._size
            sm = self._op(self._d[right], sm)

        return 0

    def _update(self, k: int) -> None:
        self._d[k] = self._op(self._d[2 * k], self._d[2 * k + 1])

def op(l, r):
	return (l[0] + r[0], min(l[0] + r[1], l[1] + r[4]), min(l[0] + r[2], l[1] + r[5], l[2] + r[7]), min(l[0] + r[3], l[1] + r[6], l[2] + r[8], l[3] + r[9]), l[4] + r[4], min(l[4] + r[5], l[5] + r[7]), min(l[4] + r[6], l[5] + r[8], l[6] + r[9]), l[7] + r[7], min(l[7] + r[8], l[8] + r[9]), l[9] + r[9])

e = (0, 0, 0, 0, 0, 0, 0, 0, 0, 0)

d = defaultdict(tuple)
d['A'] = (0, 0, 0, 0, 1, 1, 1, 1, 1, 1)
d['B'] = (1, 0, 0, 0, 0, 0, 0, 1, 1, 1)
d['C'] = (1, 1, 0, 0, 1, 0, 0, 0, 0, 1)
d['D'] = (1, 1, 1, 0, 1, 1, 0, 1, 0, 0)

N, Q = map(int, input().split())
S = input()
v = [d[S[i]] for i in range(N)]
seg = SegTree(op, e, v)
for _ in range(Q):
	t, a, b = input().split()
	if t == '1':
		a = int(a) - 1
		seg.set(a, d[b[0]])
	else:
		a = int(a) - 1
		b = int(b) - 1
		print(seg.prod(a, b + 1)[3])