N, K = map(int,input().split())
S = [int(s) for s in input()]

pt = 0
mon = 0
cnt = 0
P = []
P2 = []
while cnt < N and pt < N:
    if pt == 0:
        mon += 1
        pt += S[cnt % N]
        P.append(cnt)
        cnt += 1
        if cnt >= K:
            print(len(P))
            exit()
    while cnt < N and pt > 0 and pt < N:
        pt += S[cnt % N] - 1
        cnt += 1
        if cnt >= K:
            print(len(P))
            exit()

while cnt < N * 2:
    if pt == 0:
        mon += 1
        pt += S[cnt % N]
        P2.append(cnt % N)
        cnt += 1
    while cnt < 2 * N and pt > 0:
        pt += S[cnt % N]
        cnt += 1
        pt -= 1

if len(P2) == 0:
    print(len(P))
    exit()
'''
1巡目
len(P)払ってN+P2[0]個買う
2巡目以降
N個あたりlen(P2)払う 
↓
K -= N + P2[0]
ans += K // N * len(P2) 払う
x = K % N 余る
bisect(P2,x)払う　
'''
from bisect import bisect_left
ans = len(P)
K -= N + P2[0]
t = K // N
ans += t * len(P2)
ans += bisect_left(P2,K % N)
print(ans)