#include <bits/stdc++.h>
using namespace std;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
using Int = long long;
const char newl = '\n';

//INSERT ABOVE HERE
signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);


  int l,r;
  cin>>l>>r;

  vector<int> cnt(r+1,0);
  for(int i=l;i<=r;i++)
    for(int j=i+i;j<=r;j+=i)
      cnt[j]=1;

  int ans=0;
  for(int i=l+1;i<=r;i++)
    if(!cnt[i]) ans++;

  cout<<ans<<endl;
  return 0;
}