def root(x):
  p=x
  l=[p]
  while r[p]!=p:
    p=r[p]
    l+=[p]
  for p in l:
    r[p]=l[-1]
  return r[x]

def union(x,y):
  rx=root(x)
  ry=root(y)
  if rx==ry:
    return
  if rx>ry:
    rx,ry=ry,rx
  r[ry]=rx
  return

L,R=map(int,input().split())
r=list(range(R+1))
g=0
for i in range(L,R+1):
  for j in range(i+i,R+1,i):
    a=i
    b=j
    if root(a)!=root(b):
      g+=0
      union(a,b)
for i in range(L,R):
  a=i
  b=i+1
  if root(a)!=root(b):
    g+=1
    union(a,b)
print(g)