L,R=map(int,input().split())
e=[]
for i in range(L,R+1):
  for j in range(i+i,R+1,i):
    if L<=i<j<=R:
      e+=[(0,i,j)]
  if i+1<=R:
    e+=[(1,i,i+1)]
e.sort()

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

r=list(range(R+1))
g=0
for c,a,b in e:
  if root(a)!=root(b):
    g+=c
    union(a,b)
print(g)