import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

def main():
    n, k = MI()
    aa = list(map(int, list(sys.stdin.readline())[:-1]))
    cumsum = [0]
    for a in aa * 2:
        cumsum.append(cumsum[-1] + a)
    s = cumsum[n]
    l = 0
    r = k + 1
    while l + 1 < r:
        buy = (l + r) // 2
        now = buy
        prize = 0
        sold = 0
        while 1:
            box, bar = divmod(now, n)
            now = box * s + cumsum[sold + bar] - cumsum[sold]
            if now == 0: break
            prize += now
            if buy + prize >= k: break
            sold = (sold + bar) % n
        if buy + prize >= k:
            r = buy
        else:
            l = buy
    print(r)

main()