class SegmentTreeBase_:
    def ope(self, l, r):
        raise NotImplementedError

    def e(self):
        raise NotImplementedError

    def __init__(self, n, init=None):
        self.n = n
        self.n0 = 1 << (n - 1).bit_length()
        self.data = [self.e()] * (2 * self.n0)
        if init is not None:
            for i in range(n):
                self.data[self.n0 + i] = init[i]
            for i in range(self.n0 - 1, 0, -1):
                self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])

    def build(self):
        for i in range(self.n0 - 1, 0, -1):
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])

    def set(self, i, x):
        i += self.n0
        self.data[i] = x
        while i > 1:
            i >>= 1
            self.data[i] = self.ope(self.data[2 * i], self.data[2 * i + 1])

    def get(self, i):
        return self.data[i + self.n0]

    def __getitem__(self, i):
        return self.data[i + self.n0]

    def __setitem__(self, i, x):
        self.set(i, x)

    def prod(self, l, r):
        assert 0 <= l <= r <= self.n0
        l += self.n0
        r += self.n0
        lles = self.e()
        rres = self.e()
        while l < r:
            if l & 1:
                lles = self.ope(lles, self.data[l])
                l += 1
            if r & 1:
                r -= 1
                rres = self.ope(self.data[r], rres)
            l >>= 1
            r >>= 1
        return self.ope(lles, rres)

    def max_right(self, l, f):
        if l == self.n:
            return self.n
        l += self.n0
        sm = self.e()
        while 1:
            while l % 2 == 0:
                l >>= 1
            if not f(self.ope(sm, self.data[l])):
                while l < self.n0:
                    l <<= 1
                    if f(self.ope(sm, self.data[l])):
                        sm = self.ope(sm, self.data[l])
                        l += 1
                return l - self.n0
            sm = self.ope(sm, self.data[l])
            l += 1
            if l & -l == l:
                break
        return self.n

    def min_left(self, r, f):
        if r == 0:
            return 0
        r += self.n0
        sm = self.e()
        while 1:
            r -= 1
            while r > 1 and r % 2:
                r >>= 1
            if not f(self.ope(self.data[r], sm)):
                while r < self.n0:
                    r = 2 * r + 1
                    if f(self.ope(self.data[r], sm)):
                        sm = self.ope(self.data[r], sm)
                        r -= 1
                return r + 1 - self.n0
            sm = self.ope(self.data[r], sm)
            if r & -r == r:
                break
        return 0


class segtree(SegmentTreeBase_):
    def ope(self, l, r):
        ret = [0] * 16
        for i in range(4):
            for j in range(i, 4):
                x = 0
                for k in range(i, j + 1):
                    x = max(x, l[i * 4 + k] + r[k * 4 + j])
                ret[i * 4 + j] = x
        return tuple(ret)

    def e(self):
        return (0,) * 16


n, Q = map(int, input().split())
S = input()
a = [0] * 16
b = [0] * 16
c = [0] * 16
d = [0] * 16
for i in range(4):
    for j in range(i, 4):
        if i <= 0 <= j:
            a[i * 4 + j] = 1
        if i <= 1 <= j:
            b[i * 4 + j] = 1
        if i <= 2 <= j:
            c[i * 4 + j] = 1
        if i <= 3 <= j:
            d[i * 4 + j] = 1

tup_a = tuple(a)
tup_b = tuple(b)
tup_c = tuple(c)
tup_d = tuple(d)

data = [None] * n
for i, s in enumerate(S):
    if s == "A":
        data[i] = tup_a
    elif s == "B":
        data[i] = tup_b
    elif s == "C":
        data[i] = tup_c
    else:
        data[i] = tup_d


seg = segtree(n, data)

for _ in range(Q):
    query = input().split()
    if query[0] == "1":
        x, c = int(query[1]) - 1, query[2]
        if c == "A":
            seg.set(x, tup_a)
        elif c == "B":
            seg.set(x, tup_b)
        elif c == "C":
            seg.set(x, tup_c)
        else:
            seg.set(x, tup_d)
    else:
        l, r = map(int, query[1:])
        print(r - l + 1 - seg.prod(l - 1, r)[3])