class SegTree:
    def __init__(self, op, e, lst):
        self.n = len(lst)
        self.N0 = 2 ** (self.n - 1).bit_length()
        self.op = op
        self.e = e
        self.data = [e] * (2 * self.N0)
        if type(lst) is list:
            for i in range(self.n):
                self.data[self.N0 + i] = lst[i]
            for i in range(self.N0 - 1, 0, -1):
                self.data[i] = self.op(self.data[2*i], self.data[2*i+1])
    
    def get(self, i):
        return self.data[self.N0+i]
    
    def set(self, i, x):
        i += self.N0
        self.data[i] = x
        while i > 1:
            i >>= 1
            self.data[i] = self.op(self.data[2*i], self.data[2*i+1])
    
    def prod(self, l, r):
        if r <= l:
            return self.e
        lres = self.e
        rres = self.e
        l += self.N0
        r += self.N0
        while l < r:
            if l & 1:
                lres = self.op(lres, self.data[l])
                l += 1
            if r & 1:
                r -= 1
                rres = self.op(self.data[r], rres)
            l >>= 1
            r >>= 1
        return self.op(lres, rres)

import sys
input = sys.stdin.readline
inf = 10**6
N,Q = map(int, input().split())
S = input()
alp = {"A":0,"B":1,"C":2,"D":3}
da = [0, 0, 0, 0, 1, 1, 1, 1, 1, 1]
db = [1, 0, 0, 0, 0, 0, 0, 1, 1, 1]
dc = [1, 1, 0, 0, 1, 0, 0, 0, 0, 1]
dd = [1, 1, 1, 0, 1, 1, 0, 1, 0, 0]

p = [0,3,5,6]
D = []
for i in S:
    if i == "A":
        D.append(da) 
    elif i == "B":
        D.append(db)
    elif i == "C":
        D.append(dc)
    else:
        D.append(dd)

def op(X,Y):
    res = [inf]*10
    for i in range(4):
        for j in range(i,4):
            for k in range(i,j+1):
                res[p[i]+j] = min(X[p[i]+k]+Y[p[k]+j],res[p[i]+j]) 
    return res

e = [0]*10
st = SegTree(op, e, D)

ans = []
for _ in range(Q):
    t,x,c = input().split()
    if t == "1":
        x = int(x)-1
        if c == "A":
            st.set(x,da) 
        elif c == "B":
            st.set(x,db)
        elif c == "C":
            st.set(x,dc)
        else:
            st.set(x,dd)
    else:
        x,c = int(x)-1,int(c)
        res = st.prod(x,c)
        ans.append(min(res))

print(*ans, sep = "\n")