L,R = map(int,input().split())

dat = [0] * (R + 1)
for i in range(L,R+1):
    for j in range(i*2,R+1,i):
        dat[j] = 1
ans = 0
for u in range(R,L,-1):
    if dat[u] == 1:
        pass
    else:
        ans += 1
print(ans)