import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

import typing

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 = (self._n-1).bit_length()
        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(a, b):
    c = [inf]*16
    for i in range(4):
        for j in range(i, 4):
            for k in range(j,4):
                v=a[i*4+j]+b[j*4+k]
                if v<c[i*4+k]:c[i*4+k]=v
    return c

n, q = LI()
s = [ord(c)-65 for c in SI()]

row = [1]*16
for i in range(4): row[i*4+i] = 1
arr = [[1-(i<=c<=j) for i in range(4) for j in range(4)] for c in s]
# print(arr)
st = SegTree(op, [0]*16, arr)
for _ in range(q):
    t, x, c = SI().split()
    if t == "1":
        x = int1(x)
        c = ord(c)-65
        if s[x] == c: continue
        s[x] = c
        cur = [1-(i<=c<=j) for i in range(4) for j in range(4)]
        st.set(x, cur)
    else:
        l, r = int1(x), int(c)
        ans = st.prod(l,r)[3]
        print(ans)