INF = 10 ** 9

def e():
    return (0, 0, 0, 0, 0, 0, 0, 0, 0, 0)

def op(a, b):
    a00, a01, a02, a03, a11, a12, a13, a22, a23, a33 = a
    b00, b01, b02, b03, b11, b12, b13, b22, b23, b33 = b
    return (
        a00 + b00,
        min(a00 + b01, a01 + b11),
        min(a00 + b02, a01 + b12, a02 + b22),
        min(a00 + b03, a01 + b13, a02 + b23, a03 + b33),
        a11 + b11,
        min(a11 + b12, a12 + b22),
        min(a11 + b13, a12 + b23, a13 + b33),
        a22 + b22,
        min(a22 + b23, a23 + b33),
        a33 + b33
    )

c2mat = [
    (0,0,0,0,1,1,1,1,1,1),
    (1,0,0,0,0,0,0,1,1,1),
    (1,1,0,0,1,0,0,0,0,1),
    (1,1,1,0,1,1,0,1,0,0)
]

def solve():
    n, q = map(int, input().split())
    s = [ord(c) - 65 for c in input()]
    lg = (n - 1).bit_length()
    sz = 1 << lg
    d = [(1,) * 10] * (2 * sz)
    for i in range(n):
        d[sz + i] = c2mat[s[i]]
    for i in range(sz - 1, 0, -1):
        d[i] = op(d[i<<1], d[i<<1|1])
    for _ in range(q):
        t, x, c = input().split()
        if t == '1':
            x = sz + int(x) - 1
            c = ord(c) - 65
            d[x] = c2mat[c]
            x >>= 1
            while x:
                d[x] = op(d[x<<1], d[x<<1|1])
                x >>= 1
        else:
            l = sz + int(x) - 1
            r = sz + int(c)
            sl = e()
            sr = e()
            while l < r:
                if l & 1:
                    sl = op(sl, d[l])
                    l += 1
                if r & 1:
                    r -= 1
                    sr = op(d[r], sr)
                l >>= 1
                r >>= 1
            print(op(sl, sr)[3])
solve()