import sys
input = sys.stdin.readline

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

USE=[0]*(N+1)
Q=[]
ANS=0

for s in S:
    USE[s]=1
    Q.append(s)
    ANS+=1

while Q:
    x=Q.pop()
    for s in S:
        k=A[s+x]

        if USE[k]==1:
            continue
        USE[k]=1
        Q.append(k)
        ANS+=1

print(ANS)