#include <iostream>
using namespace std;

int main(void)
{
	const  int MAX = 1000000;
	int number =0;
	int count = 0;
	bool noPrim[MAX];
	int p_count=0;

	for(int i=0;i<MAX;i++){
		noPrim[i]=false;
	}
	int j;
	for(int i=2;i<MAX;i++){
		if(noPrim[i]==true)break;
		j=i*2;
		while(j<MAX){
			noPrim[j]=true;
			j+=i;
		}
	}
	while(cin >>  number){
		count = 0;
		for(int i=2;i<=number;i++){
			if(noPrim[i]==false)count++;
		}
		cout << count << endl;
	}
	return 0;
}