def checknext(plc, cnt):
    global b
    c = cnt
    c += int(S[plc % N])
    j = plc + 1
    if j < K:
        if c == 0:
            b += 1
            checknext(j, c)
        else:
            c -= 1
            checknext(j, c)
    else:
        print(b)
N, K = map(int, input().split())
S = input()
b = 1
checknext(0, 0)