import sys
input = sys.stdin.readline

N,Q=map(int,input().split())

C=[[0,0],[0,1],[0,2],[0,3],[1,1],[1,2],[1,3],[2,2],[2,3],[3,3]]

LIST=[[-1]*4 for i in range(4)]

for i in range(len(C)):
    x,y=C[i]
    LIST[x][y]=i
    
def seg_function(x,y): # Segment treeで扱うfunction
    #print(x,y)
    ANS=[1<<30]*10

    for i in range(10):
        for j in range(10):
            a,b=C[i]
            c,d=C[j]

            if b<=c:
                k=LIST[a][d]
                ANS[k]=min(ANS[k],x[i]+y[j])
    return ANS
                

seg_el=1<<(N.bit_length()) # Segment treeの台の要素数
SEG=[[1<<30]*10 for i in range(2*seg_el)] # 1-indexedなので、要素数2*seg_el.Segment treeの初期値で初期化

def update(n,x,seg_el): # A[n]をxへ更新
    i=n+seg_el
    SEG[i]=x
    i>>=1 # 子ノードへ
    
    while i!=0:
        SEG[i]=seg_function(SEG[i*2],SEG[i*2+1])
        i>>=1
        
def getvalues(l,r): # 区間[l,r)に関するseg_functionを調べる
    L=l+seg_el
    R=r+seg_el
    ANS1=[0]*10
    ANS2=[0]*10

    while L<R:
        if L & 1:
            ANS1=seg_function(ANS1, SEG[L])
            L+=1

        if R & 1:
            R-=1
            ANS2=seg_function(SEG[R], ANS2)
        L>>=1
        R>>=1

    return seg_function(ANS1, ANS2)

S=input().strip()
AX=[]

for i in range(4):
    X=[1]*10
    for j in range(i+1):
        for k in range(i,4):
            X[LIST[j][k]]=0

    #print(X)
    AX.append(X)

for i in range(len(S)):
    update(i,AX[ord(S[i])-65],seg_el)

for tests in range(Q):
    x,y,z=input().split()

    if int(x)==1:
        y=int(y)-1

        update(y,AX[ord(z)-65],seg_el)
    else:
        ANS=getvalues(int(y)-1,int(z))
        print(min(ANS))