import sys
input = sys.stdin.readline

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

now=1200
AC=0

for i in range(N):
    s=S[i]
    if s=="1":
        if now==1200:
            pass
        else:
            now+=1
            AC+=1

            if AC==A:
                print(i+1)
                exit()
    else:
        now-=1

now2=now
A-=AC
ANS=N

AC=0

for i in range(N):
    s=S[i]
    if s=="1":
        if now==1200:
            pass
        else:
            now+=1
            AC+=1

            if AC==A:
                print(ANS+i+1)
                exit()
    else:
        now-=1


if A%AC==0:
    k=A//AC-1
else:
    k=A//AC
ANS+=N*k
A-=AC*k

#print(ANS,A,AC)

AC=0

for i in range(N):
    s=S[i]
    if s=="1":
        if now==1200:
            pass
        else:
            now+=1
            AC+=1

            if AC==A:
                print(ANS+i+1)
                exit()
    else:
        now-=1