#include <iostream>
using namespace std;

int v[200030];

int main(){
  long long n,m; cin >> n >> m;
  if (n==1){cout << 0 << endl; return 0;}
  for (long long i = 0; i < 200010; i++) {
    v[i] = 0;
  }
  for (long long i = n; i < (m + 20) ; i++) {
    if (v[i] == 1) continue;
    for (long long x = i * 2; x < m + 2; x += i){
      v[x] = 1;
    }
  }
  long long ans = 0;
  for (long long i = n; i < m + 1; i++) {
    if (v[i] == 0) ans++;
    // cout << "v[" << i << "] = " << v[i] << endl;
  }
  cout << ans - 1 << endl;
}