import sequtils,strutils,math
var N, K : int
(N, K) = stdin.readline.split.map(parseInt)
proc ctoi(c : char):int =
    return c.int - '0'.int

var
    S = stdin.readline
    cnt : array[2,int]
    cnta : int
    ans : int
    cnt2 : array[51,int]
for i in 0..1:
    for j,s in S:
        if cnta == 0:
            cnt[i] += 1
        else:
            cnta -= 1
        if (i == 1 and N < K) or (i == 0 and N >= K):
            cnt2[j + 1] = cnt[i]
        cnta += s.ctoi
if cnt[0] == cnt[1] or K <= N:
    ans = K div N * cnt[0] + cnt2[K mod N]
else:
    ans = cnt[0] + (K div N - 1) * cnt[1] + cnt2[K mod N]
echo ans