l,r = map(int,input().split())
if l == 1:
    print(0)
    exit()
graph = [[] for i in range(r+1)]
vis = [0 for i in range(r+1)]
for i in range(l,r+1):
    if vis[i] == 0:
        vis[i] = 1
        for j in range(2*i,r+1,i):
            vis[j] = 1
            graph[i].append(j)
            graph[j].append(i)
stack = []
ans = 0
for i in range(l,r+1):
    if vis[i] == 1:
        ans += 1
        stack.append(i)
        vis[i] += 1
        while stack:
            x = stack.pop()
            for y in graph[x]:
                if vis[y] == 1:
                    stack.append(y)
                    vis[y] = 2
print(ans-1)