N, K = map(int,input().split())
S = input()

must = [False] * N
atari = 0
buy = 0
if N > K :
    for i in range(N):
        if S[i] == '0':
            if atari > 0:
                atari -= 1
            else:
                buy += 1

        elif S[i] == '1':
            if atari > 0 :
                atari -= 1
            else:
                buy += 1
            atari += 1
        
        else :
            if atari > 0:
                atari -= 1
            else:
                buy += 1
            atari += 2

        if i+1 == K:
            break

else:
    for i in range(N):
        if S[i] == '0':
            if atari > 0:
                atari -= 1
            else:
                must[i] = True

        elif S[i] == '1':
            if atari > 0 :
                atari -= 1
            else:
                must[i] = True
            atari += 1
        
        else :
            if atari > 0:
                atari -= 1
            else:
                must[i] = True
            atari += 2

    count  = 0
    for i in range(N):
        if must[i]:
            count += 1
            
    l = K % N

    atariend = atari
    
    for i in range(l):
        if S[i] == '0':
            if atariend > 0:
                atariend -= 1

        elif S[i] == '1':
            if atariend > 0 :
                atariend -= 1
            atariend += 1
        
        else :
            if atariend > 0:
                atariend -= 1

        countend = 0

    for i in range(l):
        if must[i]:
            countend += 1

    if atari >= count :
        buy = count
    else:
        if l == 0:
            buy = count + (count - atari) * (K // N - 1)
        
        else :
            buy = count + (count - atari) * (K // N - 1) + countend
            
print(buy)