#include <algorithm>
#include <map>
#include <vector>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstring>
#include <cctype>
#include <cstdlib>
#include <cmath>
#include <string>
#include <queue>
using namespace std;

#define REP(i,n) for(int i=0; i<n; ++i)
#define IREP(it,array) for(vector<int>::iterator it=array.begin(); it!=array.end(); ++it)
#define SREP(it,array) for(vector<string>::iterator it=array.begin(); it!=array.end(); ++it)
#define MP make_pair
typedef long long LL;


int main()
{
  cout.setf(ios::fixed, ios::floatfield);
  cout.precision(6);

  int INF = 1000000;

  int n;
  while(cin>>n){
    int res=0;
    bool notPrime[n+1];
    memset(notPrime,0,sizeof(notPrime));
    
    notPrime[0] = notPrime[1] = true;

    for(int i=2; i<=n; i++){
      if(!notPrime[i]){
	res++;
	for(int j=2*i; j<=n; j+=i){
	  notPrime[j] = true;
	}
      }
    }
    cout << res << endl;
  }


  return 0;
}