#include<iostream>
#include<cstdio>
#include<algorithm>
//#define int long long
using namespace std;
int l,r,prime[30000050],vis[30000050],k,Fool;
void Prime(int n)
{
	for(register int i=2;i<=n;++i) {
		if(!vis[i]) prime[++prime[0]]=i;
		for(register int j=1;i*prime[j]<=n+1;++j) {
			vis[i*prime[j]]=1;
			if(i%prime[j]==0) break;
		}
	}
}
signed main()
{
	register int j;
	cin>>l>>r;
	Prime(r);
	k=l;
	for(register int i=1;i<=prime[0];++i) {
		l=k;
		for(j=l;j<=r;++j) {
			if(j>prime[i]) break;
			k++;
			if(j==prime[i]) Fool++;
		}
	}
	cout<<Fool;
	return 0;
}