N,A = list(map(int,input().split()))
S = input()

now = 0
for i in range(N):
    if(S[i] == "0"):
        now -= 1
    else:
        if(now < 0):
            A -= 1
            if(A == 0):
                print(i+1)
                exit()
            now += 1

solve_per_N = 0
for i in range(N):
    if(S[i] == "0"):
        now -= 1
    else:
        if(now < 0):
            solve_per_N += 1
            now += 1

ans = N + (A-1)//solve_per_N * N
A = (A-1)%solve_per_N + 1

for i in range(N):
    if(S[i] == "0"):
        now -= 1
    else:
        if(now < 0):
            A -= 1
            if(A == 0):
                print(ans+i+1)
                exit()
            now += 1