#!/usr/bin/ruby
N,K=gets.split.map(&:to_i)
D,R=(K-1).divmod(N)
R+=1
S=gets.chomp.chars.map(&:to_i)

#phase1: brute force
buy=[0]*(N+1)
buy[0]=0
atari=0
cur=0
0.step(N-1){|i|
	if atari==0
		atari+=1
		buy[i+1]=1
	end
	atari+=S[i]-1
}
1.step(N){|i|
	buy[i]+=buy[i-1]
}
#p buy
if D==0
	p buy[R]
elsif D==1
	p buy[-1]+[buy[R]-atari,0].max
else
	p buy[-1]+(D-1)*[buy[-1]-atari,0].max+[buy[R]-atari,0].max
end