N,K=map(int,raw_input().split())
S=raw_input()
dp=[0 for i in range(2*N+1)]
rest=0
prev=0
for i in range(1,2*N+1):
    if rest == 0:
        dp[i]=dp[i-1]+1
        rest += ord(S[(i-1)%N])-ord("0")
    else:
        rest-=1
        dp[i]=dp[i-1]
        rest += ord(S[(i-1)%N])-ord("0")
#print dp[(K-1)%N+1],((K-(K-1)%N-1)/N),(dp[(K-1)%N+1+N]-dp[(K-1)%N+1])
print dp[(K-1)%N+1]+((K-(K-1)%N-1)/N)*(dp[(K-1)%N+1+N]-dp[(K-1)%N+1])