# your code goes here

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

must = [False] * N

buy = 1
atari = 0
i = 0
l = 0

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


l = K % N

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

must = [False] * N
atariend = atari
for x in range(l):
    if S[i] == '0':
        if atariend > 0:
            atariend -= 1
        else:
            must[i] = True
            
    elif S[i] == '1':
        if atariend > 0 :
            atariend -= 1
        else:
            must[i] = True
        atariend += 1
    
    else :
        if atariend > 0:
            atariend -= 1
        else:
            must[i] = True
        
        atariend += 2

countend = 0
for i in range(l):
    if must[i]:
        countend += 1

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