def scan; gets.split.map(&:to_i);end

def ok(e)
    p e;exit
end

n,k = scan
s = gets.chomp.chars.map!(&:to_i)

i = 0
r = 0
b = 0
s.each{|e|
    if 0<b
        b-=1
    else
        r+=1
    end
    b+=e
    i+=1
    ok r if k<=i
}

r2 = 0
b2 = b
s.each{|e|
    if 0<b
        b-=1
    else
        r2+=1
    end
    b+=e
    i+=1
    ok r+r2 if k<=i
}

k2 = k%n
rr = r+(k/n-1)*r2

b2 = b
i=0
s.each{|e|
    ok rr if k2<=i
    if 0<b
        b-=1
    else
        rr+=1
    end
    b+=e
    i+=1
}
ok rr