n,k = map(int,input().split())
A = list(map(int,input()))

inf = 10**10
doubling = [[0]*55 for i in range(33)]
for i in range(n):
    bar = 1
    count = 0
    now = i
    while bar:
        count += 1
        if count == 100:
            break
        bar += A[now]-1
        now += 1
        now %= n
    if count == 100:
        doubling[0][i] = inf
    else:
        doubling[0][i] = count


for i in range(1,33):
    for j in range(50):
        nex = (doubling[i-1][j]+j)%n
        doubling[i][j] = doubling[i-1][j]+doubling[i-1][nex]
        doubling[i][j] = min(doubling[i][j],inf)

ans = 0
now = 0
for i in range(33)[::-1]:
    if k >= doubling[i][now]:
        k -= doubling[i][now]
        ans += 1<<i
        now += doubling[i][now]
        now %= n

if k:
    ans += 1
print(ans)