num1,num2=map(int,input().split())
n=[]
for i in range(num1+1,num2+1):
  if i>1:
    for v in range(2,i):
      if(i%v==0):
        break
    else:
      n.append(v)
print(len(n)+1)

0bf74afcf402fd53bceb964876a6fbd0083a710a
<mask token>

<mask token>
for i in range(num1 + 1, num2 + 1):
    if i > 1:
        for v in range(2, i):
            if i % v == 0:
                break
        else:
            n.append(v)
print(len(n) + 1)

num1, num2 = map(int, input().split())
n = []
for i in range(num1 + 1, num2 + 1):
    if i > 1:
        for v in range(2, i):
            if i % v == 0:
                break
        else:
            n.append(v)
print(len(n) + 1)

num1,num2=map(int,input().split())
n=[]
for i in range(num1+1,num2+1):
  if i>1:
    for v in range(2,i):
      if(i%v==0):
        break
    else:
      n.append(v)
print(len(n)+1)
