import sys

def LI(): return list(map(int, sys.stdin.readline().split()))

n,m=LI()
aa=LI()
ss=LI()
tt=set(ss)
st=list(ss)
while st:
    j=st.pop()
    for i in ss:
        a=aa[i+j]
        if a in tt:continue
        tt.add(a)
        st.append(a)
print(len(tt))