def buy_box(ice_box, buy=0, hit=0):
    for ice in ice_box:
        if hit>0:hit-=1
        else:buy+=1
        hit+=ice
    return buy,hit
def main():
    box_len,full=map(int,input().split())
    ice_box=[int(i) for i in input()]
    if box_len>=full:print(buy_box(ice_box[:full])[0])
    else:
        buy,hit=buy_box(ice_box)
        if hit>=box_len:print(buy)
        else:print(buy+buy_box(ice_box,hit=hit)[0]*(full//box_len-1)+buy_box(ice_box[:full%box_len],hit=hit)[0])
main()