class SegTree:
    def __init__(self, op, e, lst):
        if type(lst) is int:
            self.n = lst 
        else:
            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 update(self, i, x): #a_iの値をxに更新
        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 add(self, i, x):
        i += self.N0
        self.data[i] = self.op(x, self.data[i])
        while i > 1:
            i >>= 1
            self.data[i] = self.op(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.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)

inf = 1<<60
N,Q = map(int, input().split())
S = input()

def make_matrix(c):
    x = ord(c) - ord("A")
    A = [[inf]*4 for i in range(4)]
    for i in range(4):
        for j in range(i,4):
            if i <= x <= j:
                A[i][j] = 0
            else:
                A[i][j] = 1
    return A

D = []
for i in range(N):
    D.append(make_matrix(S[i]))

def op(X,Y):
    res = [[inf]*4 for i in range(4)]
    for i in range(4):
        for j in range(i,4):
            for k in range(i,j+1):
                res[i][j] = min(X[i][k]+Y[k][j], res[i][j]) 
    return res
e = [[0]*4 for i in range(4)]
st = SegTree(op, e, D)

for _ in range(Q):
    t,x,c = input().split()
    
    if t == "1":
        x = int(x)-1
        st.set(x,make_matrix(c))
    else:
        l,r = int(x)-1,int(c)
        res = st.prod(l,r)
        
        ans = inf
        for i in range(4):
            ans = min(ans,min(res[i]))
        print(ans)